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THIS  VOLUME  IS  AFFECTIONATELY  DEDICATED 


47016 


PREFACE  TO  SECOND  EDITION. 


The  call  for  a  second  edition  has  made  it  possible  to 
make  changes  arid  additions  in  the  text. 

In  the  Circulatory  System  additions  were  made,  among 
the  most  important  of  which  are  the  Bundle  of  His,  Hemo- 
lymphnodes  and  the  Parasympathetic  Bodies. 

Part  of  the  chapter  on  the  Nerve  System  was  rewritten 
and  several  cuts  were  added. 

In  order  to  make  this  book  of  greater  use  to  the  dental 
students,  the  Histology  of  the  Tooth  was  rewritten  and  en- 
larged upon,  and  a  new  chapter  on  the  Development  of  the 
Face  and  Teeth,  with  appropriate  cuts,  was  added. 

The  writer  desires  to  thank  the  teachers  and  students 
who  have  seen  fit  to  use  this  work,  and  he  hopes  that  the 
present  edition  will  meet  with  the  same  satisfaction. 

914  SOUTH  FORTY- SEVENTH  STREET, 
PHILADELPHIA,  October,  1909. 


Vll 


PREFACE  TO  FIRST  EDITION. 


IT  has  been  the  author's  purpose  to  supply  a  volume 
more  complete  than  the  existing  compends,  and  yet  not  so 
voluminous  as  a  Text-book.  An  effort  has  been  made  to 
present  the  matter  in  a  clear  and  concise  manner,  and  as 
up-to-date  as  possible. 

The  subject  of  Embryology  has  been  touched  upon  only 
in  so  far  as  it  bears  directly  upon  the  Histology. 

The  chapter  on  Technic  has  been  made  as  complete 
as  is  necessary  for  routine  histologic  and  pathologic  work. 
The  Connective  Tissues  have  been  grouped  in  what  seems  a 
simple  and  also  characteristic  manner.  The  Blood  Cells 
have  also  been  arranged  in  a  simple  and  readily-compre- 
hended form. 

The  chapter  on  Placenta  and  Umbilical  Cord  has,  how- 
ever, been  written  somewhat  in  detail,  as  the  embryology 
of  these  organs  is  essential  for  a  thorough  knowledge  of 
their  structure.  The  illustrations  are  from  the  works  of 
Prof.  Minot,  to  whom  the  writer  is  indebted  for  their  use. 

The  forty-seven  new  cuts  were  prepared  ^nder  the 
direction  of  Dr.  H.  H.  Cushing.  Of  these,  twenty-seven 
are  from  slides,  while  the  remainder  represent  modifications 
of  current  Text-book  figures. 

The  writer  desires  to  thank  Dr.  R.  C.  Rosenberger  for 
his  assistance  in  proof-reading  and  suggestions,  and  the 
publishers  for  their  many  kindnesses  and  courtesies. 

914  SOUTH  FORTY-SEVENTH  STREET, 
PHILADELPHIA. 


CONTENTS. 


CHAPTER  I. 
Technic     . 


CHAPTER  II. 

The  Cell   ' 31 

CHAPTER  III. 
The  Tissues — Epithelial  Tissues     45 

CHAPTER  IV. 

Connective  Tissues 58 

CHAPTER  V. 

Muscle  Tissues    .  .  .• 78 

CHAPTER  VI. 

Nerve  Tissues 84 

CHAPTER  VII. 
Circulatory  System 96 

CHAPTER  VIII. 
Lymphatic  System 112 

CHAPTER  IX. 
Alimentary  Tract      1 18 

CHAPTER  X. 

Digestive  Glands    148 

xi 


xii  CONTENTS. 

CHAPTER  XL  PAGE 

Respiratory  System  and  Thyroid  Body 159 

CHAPTER  XII. 
Urinary  System  and  Adrenal      171 

CHAPTER  XIII. 
Male  Genital  System 186 

CHAPTER  XIV. 

Female  Genital  System   201 

CHAPTER  XV. 

Placenta  and  Umbilical  Cord   217 

CHAPTER  XVI. 

Skin  and  Its  Appendages    230 

CHAPTER  XVII. 
Nerve  System   ' 245 

CHAPTER  XVIII. 

Eyeball  and  Lacrimal  Apparatus 274 

CHAPTER  XIX. 
The  Ear   298 

CHAPTER  XX. 

The  Senses  of  Smell,  Taste  and  Touch      311 

CHAPTER  XXI. 

Development  of  Face  and  Teeth 318 

INDEX 333 


LIST  OF  ILLUSTRATIONS. 


1.  The  Cell 32 

2.  Karyokinesis,' Close  Coil 35 

3.  Karyokinesis,  Loose  Coil 36 

4.  Karyokinesis,  Equatorial  Plate 37 

5.  Karyokinesis,  Nuclear  Spindle 38 

6.  Karyokinesis,  Daughter  Stars 39 

7.  Karyokinesis,  Daughter  Cells    39 

8.  Unripened  Ovum  of  a  Young  Guinea-pig   41 

9.  Simple  Squamous  and  Cuboidal  Epithelial  Cells 46 

10.  Squamous  Cells  of  Frog's  Skin  (surface  view) 46 

11.  Squamous  Cell,  Isolated     46 

12.  Stratified  Squamous  Epithelium     46 

13.  Simple  Columnar,  Ciliated  and  Goblet  Cells 47 

14.  Isolated  Columnar  and  Ciliated  Cells;  Goblet  Cells  in 

Various  Stages 47 

1 5.  Pseudostratified  Cells 48 

1 6.  Stratified  Columnar,  Ciliated  and  Goblet  Cells     49 

17.  Transitional  Cells    49 

1 8.  Various  Forms  of  Endothelial  Cells 50 

19.  Simple  Tubular  Gland  from  Large  Intestine    54 

20.  Diagram  of  Tubular  Glands    55 

21.  Diagram  of  Alveolo-tubular  Glands 55 

22.  Diagram  of  Alveolar  Glands 56 

23.  Varieties  of  Connective  Tissue    60 

24.  White  Fibrous  Tissue    63 

2  5.   Varieties  of  Cartilage 68 

26.  Cross-section  of  Compact  Bone     71 

27.  Cross- section  of  Developing  Bone     76 

28.  Varieties  of  Muscle  Tissue   80 

29.  Nerve  Cells  and  Fibres 88 

30.  Tactile  Cells   90 

31.  Corpuscle  of  Meissner     91 

32.  Pacinian  Body 92 

xiii 


XIV  LIST    OF   ILLUSTRATIONS. 

FIGURE  PAGE 

33.  Tendon-spindle    93 

34.  Motor  Nerve-endings    94 

35.  Cross-section  of  a  Medium-sized  Artery    100 

36.  Cross-section  of  a  Vein 103 

37.  Forms  of  Blood  Cells    105 

38.  Hemin  Crystals 109 

39.  Hemoglobin  Crystals    iog 

40.  Section  of  a  Human  Lymph  Node      113 

41.  Section  of  the  Spleen    115 

42.  Section  of  the  Thymus  Body    117 

43.  Longitudinal  Section  of  a  Tooth     121 

44.  Cross-section  of  the  Tongue     128 

45.  Vertical  Section  of  a  Human  Tonsil    130 

46.  Cross-section  of  a  Human  Esophagus .  .  .  132 

47.  Section  of  the  Cardiac  End  of  the  Stomach 135 

48.  Section  of  the  Pyloric  End  of  the  Stomach    .  137 

49.  Section  of  the  Duodenum    139 

50.  Longitudinal  Section  of  a  Villus 140 

51.  Cross- section  of  the  Ileum     141 

52.  Cross-section  of  the  Colon 143 

53.  Cross- section  of  the  Human  Appendix    14  ^ 

54.  Section  of  Pig's  Liver     1 4<j 

55.  Section  of  Human  Pancreas    1 56 

56.  Section  of  the  Submaxillary  Gland  of  a  Fox    i  ;; 

57.  Cross- sect  ion  of  Trachea    162 

58.  Section  of  Human  Lung     164 

59.  Section  of  Human  Thyroid  Body 169 

60.  Section  of  Human  Kidney 172 

61.  Section  of  Injected  Kidney   176 

62.  Sections  of  Human  Ureter  and  Bladder 179 

63.  Section  of  Human  Adrenal    184 

64.  'Section  of  Human  Testicle    187 

65.  Diagram  of  Development  of  Spermia    IQ  i 

66.  Human  Spermia    194 

67.  Section  of  a  Human  Prostate    197 

68.  Cross-section  of  an  Ovary  of  a  Cat     202 

69.  Ovum  of  a  Woman     204 

70.  Cross-section  of  a  Human  Oviduct     209 

71.  Resting  Uterine  Mucosa 211 

72.  Cross-section  of  a  Human  Vagina    214 

73.  Diagram  of  Development  of  Primates     218 


LIST    OF    ILLUSTRATIONS.  XV 

FIGURE  T-AGE 

74.  Diagram  of  Development  of  Primates     219 

75.  Diagram  of  Development  of  Primates     221 

76.  Semi-diagrammatic  Outline  of  Uterus  and  Embryo.  .  .  .  223 

77.  Human  Placenta  at  Term    225 

78.  Cross-section  of  the  Human  Umbilical  Cord     226 

79.  Cross-section  of  the  Skin  of  the  Sole  of  the  Foot 232 

80.  Section  of  Scalp  Hair   235 

81.  Cross-section  of  a  Nail 238 

82.  Section  of  a  Lacfating  Human  Mammary  Gland     241 

83.  Vertical  Section  of  Human  Cerebral  Cortex     248 

84.  Vertical  Section  of  Human  Cerebellar  Cortex     253 

85.  Diagram  of  Transverse  Section  of  Pons     256 

86.  Diagram  of  Transverse  Section  of  Pons     257 

87.  Section  of  Oblongata  at  Midolivary  Level 260 

88.  Section  of  Oblongata  at  Motor  Decussation 261 

89.  Composite  Diagram  of  Spinal  Cord    .  . 264 

90.  Cross-section  of  Human  Spinal  Cord 266 

91.  Diagram  of  Functional  Divisions  of  Spinal  Cord 272 

92.  Corneo-scleral  Junction  of  Man     277 

93.  Vertical  Section  of  Human  Retina     283 

94.  Cells  from  the  Retina  of  an  Ape 285 

95.  Vessels  of  the  Eye     290 

96.  Section  of  the  Eyelid    293 

97.  Horizontal  Section  of  the  Internal  Ear  of  a  Kitten    ...  304 

98.  Scheme  of  the  Structure  of  the  Tympanic  Wall    305 

99.  Corti's  Organ   308 

100.  Diagram  of  Olfactory  Mucosa 312 

10 1.  Isolated  Cells  of  Olfactory  Mucosa 313 

102.  Taste-bud  from  the  Papilla  Foliata  of  a  Rabbit 314 

103.  Corpuscle  of  Wagner     315 

104.  Pacinian  Body 316 

105.  Face  of  Embryo  of  8  mm 321 

1 06.  Four  Stages  of  Tooth  Development      323 

107.  Section  of  Developing  Tooth  of  Cat  Embryo   325 


COMPEND  OF  HISTOLOGY. 


CHAPTER  I. 

..     TECHNIC. 

For  a  thorough  understanding  of  Histology  a  knowledge 
of  Technic  is  requisite,  as  sections  for  study  must  be 
properly  prepared,  and  this  requires  skill  and  care. 

The  various  steps  necessary  to  prepare  a  piece  of  tissue  for 
sectioning  are  Fixation,  Dehydration,  Clearing,  Infiltra- 
tion and  Blocking. 

FIXATION. 

Fixation  is  the  process  by  which  the  intercellular  sub- 
stance and  the  protoplasm  of  the  cells  are  coagulated  by  the 
aid  of  solutions,  thereby  keeping  them  as  nearly  like  normal 
as  possible.  Such  solutions  are  FIXING  FLUIDS,  of  which 
there  are  a  great  many  combinations.  Simple  fixatives, 
which  are  not  numerous,  will  be  given  first,  and  under  each, 
its  combinations. 

For  fixation,  one-quarter  inch  cubes  or  slices  of  organs, 
one-eighth  inch  thick  and  cut  at  intervals,  are  the  most 
satisfactory. 

i.  Heidenhain's  Solution  consists  of  a  saturated  solution 
of  bichlorid  of  mercury  in  a  normal  salt  solution. 

Bichlorid  of  mercury 112  gms. 

Sodium  chlorid       5  gms. 

Water      1000  c.c. 

Add  the  bichlorid  to  the  hot  salt  solution  and  when  dis- 
solved set  aside  to  cool.  The  excess  of  bichlorid  will  crys- 
tallize and  keep  the  solution  saturated. 


2  TECHNIC. 

Three  to  5  per  cent,  of  glacial  acetic  acid  aids  the  pene- 
tration of  the  bichlorid  and  assures  more  thorough  fixation. 

This  solution  requires  from  two  to  four  hours  to  fix  one- 
half-inch  cubes. 

2.  Potassium  Bichromate. — This  salt  in  a  solution  of 
31/2  per  cent,  strength  is  a  good  fixative  and  hardener. 
The  strength  is  gradually  increased  1/2  of  i  per  cent,  by 
frequent  renewal,  to  6  per  cent.,  in  the  course  of  six  weeks. 
It  will  not  injure  tissues  left  in  it  for  a  longer  time.  It  is  not 
often  used  alone  but  in  combinations  mentioned  below. 

a.  Zenker's   Fluid   is   a   mixture  of   Muller's  fluid   and 
bichlorid  of  mercury. 

Mailer's  fluid       1000  c.c. 

Corrosive  sublimate       112  gms. 

Mix  and  add  before  use 
Glacial  acetic  acid 50  c.c. 

This  solution  requires  from  twelve  to  twenty-four  hours 
to  act  and  should  be  freshly  prepared  each  time  before 
using. 

b.  Tellyesnicky's  Fluid  consists  of  a  3  per  cent,  solution 
of  potassium  bichromate  to  which  is  added  5  per    cent,  of 
glacial  acetic  acid   (5  c.c.  per  100).     It  is  allowed  to  act 
twelve    to    twenty-four   hours    and    then    the    tissues    are 
thoroughly   washed    and    dehydrated.     Nuclei    are    better 
preserved  by  this  solution  than  by  the  usual  bichromate 
mixtures. 

c.  Miiller's  Fluid  depends   upon   potassium   bichromate 
for  its  action.     Penetration  is  aided  by  sodium  sulphate. 

Potassium  bichromate       60  gms. 

Sodium  sulphate 30  gms. 

Water 3000  c.c. 

This  solution  requires  from  three  to  six  weeks  for  fixing, 
but  a  longer  time  does  not  injure  the  tissues.  It  is  com- 


FIXING    SOLUTIONS.  3 

• 

monly  used  in  the  dark,  and  renewed  as  often  as  it  becomes 
cloudy. 

d.  Kopsch's  Fluid  is  a  combination  of  potassium  bichro- 
mate and  formalin. 

Potassium  bichromate  (3.5%)     .    .       80  parts. 
Formalin  (40%) 20  parts. 

The  tissue  remains  in  this  solution  for  about  twenty-four 
hours,  and  is  then  transferred  to  a  3.5  per  cent,  solution  of 
potassium  bichromate  for  three  or  four  days.  It  should 
then  he  thoroughly  washed  and  dehydrated.  This  solution 
is  especially  adapted  to  the  nerve  system. 

Other  combinations  of  this  class  are  Orth's,  Erlicki's  and 
Bensley's  solutions. 

3.  Chromic  Acid  is  generally  used  in  .1   to  .5  per  cent, 
solutions,  and  should  be  allowed  to  act  one  to  eight  days,  as 
it  penetrates  slowly.     It  is  especially  adapted  to  connective 
tissues  and  where  mitotic  figures  are  to  be  studied. 

4.  Osmic  Acid. — This  reagent  is  used  in  .1  to  i  per  cent, 
solutions  as  well  as  in  combination  with  others.     It  is  a 
specific  reagent  for  adipose   tissue,   but  if   turpentine  or 
alcohol-ether  is  used  for  clearing  the  osmicated  fat  will  be 
removed.     The  time  for  fixation  depends  upon  the  strength, 
usually  from  twelve  to  twenty-four  hours  for  i  per  cent, 
solutions. 

a.  Flemming's  Solution: 

Osmic  acid  (2%  solution)  ....  4  c.c. 
Chromic  acid  (i%  solution)  ...  15  c.c. 
Glacial  acetic  acid i  c.c. 

This  is  the  stronger  solution  recommended  by  Flemming. 

This  solution  which  fixes  the  tissues  in  from  one  to  two 
days,  although  a  longer  time  will  not  injure  them,  should  be 
changed  at  least  once.  The  tissues  are  then  thoroughly 


4  TECHNIC. 

washed  and  dehydrated.     This  fluid,  which  is  good  for  the 
study  of  mitotic  figures,  should  be  prepared  just  before 
using,  as  it  does  not  keep, 
b.  Golgi's  Solution : 

Osmic  acid  (2  %  solution) 2  parts. 

Potassium  bichromate  (2  to  2.5%  solution)      ..8  parts. 

Harden  for  three  days  in  this  solution  and  impregnate 
with  silver  nitrate  solution.  This  is  used  to  stain  nerve 
cells  and  their  processes  and  glial  cells.  For  farther  step 
see  p.  17. 

5.  Formalin  is  a  saturated  solution  of  FORMALDEHYDE 
GAS  in  water.     It  is  not  used  in  full  strength,  but  usually  as 
a  4  to  10  per  cent,  solution.     A  10  per  cent,  solution  is  pre- 
pared as  follows : 

Formalin 10  c.c. 

Sodium  chlorid  (5%  solution)      .    .       go  c.c. 

This  requires  from  twelve  to  twenty-four  hours  for  its 
action,  and  is  especially  useful  in  the  nerve  system.  It 
may  be  used  with  potassium  bichromate  as  above  given. 

6.  Nitric  Acid  is  used  as  a  3  per  cent,  solution,  and  small 
pieces  of  tissue  are  allowed  to  remain  therein  from  one-half 
to  one  hour.     Large  specimens  (embryos)  require  from  four 
to  eight  hours.     After  fixation  the  tissues  are  immediately 
transferred  to  70  per  cent,  alcohol. 

It  is  especially  adapted  to  connective  tissues,  ova,  and 
embryos. 

7.  Alcohol. — There  are  several  strengths  of  alcohol  suit- 
able for  fixation.     Besides  acting  as  fixatives  they  at  the 
same  time  dehydrate. 

a.  Absolute  Alcohol. — This  should  be  of  at  least  99.2 
per  cent,  strength.  It  acts  very  rapidly  and  thoroughly,  but 


DEHYDRATION.  5 

• 

its  expense  prevents  its  routine  use.  It  must  be  changed 
several  times.  After  twenty-four  to  forty-eight  hours  the 
tissues  are  ready  to  be  cleared. 

b.  Ninety-five  Per  Cent.  Alcohol  acts  in  the  same  way  as 
the  above,  but  some  (Mallory  and  Wright)  hold  that  shrink- 
age results  if  any  solution  weaker  than  the  absolute  alco- 
hol is  used.  This  strength  has,  however,  yielded  good 
results  in  the  nerve  system.  It  must  be  frequently  re- 
newed. 

Tissues  that  have  been  fixed  in  solutions  containing  either 
osmic  acid  or  chromium  salts  must  be  thoroughly  washed  be- 
fore dehydration.  Golgi's  method  of  staining  is  an  excep- 
tion, as  will  be  seen  when  its  steps  are  considered. 

Blood  spreads  are  readily  fixed  in  a  solution  of  equal 
parts  of  absolute  alcohol  and  ether  in  which  they  are  al- 
lowed to  remain  from  twenty  minutes  to  an  hour.  Another 
good  fixative  is  absolute  alcohol,  nine  parts,  and  formalin, 
one  part.  The  time  for  fixing  is  about  the  same. 

The  blood  spreads  may  be  subjected  to  a  temperature  of 
120°  C.  for  twenty  minutes.  Ehrlich  prefers  this  method  of 
fixation  to  the  above. 

DEHYDRATION. 

After  the  tissues  have  been  fixed  in  one  of  the  above  solu- 
tions and  washed,  they  are  ready  for  the  second  step,  that 
of  Dehydration. 

Dehydration,  or  hardening,  is  the  removal  of  the  water 
from  the  tissues,  and  is  accomplished  by  alcohols  of  ascend- 
ing strengths.  The  tissues  are  transferred  to  a  FIFTY  PER 
CENT,  solution  for  six  to  twenty-four  hours,  unless  other- 
wise directed.  This  is  followed  by  immersion  in  a  SEVENTY 
PER  CENT,  solution  for  the  same  time,  and  then  in  a  NINETY- 
FIVE  PER  CENT,  solution  for  at  least  twenty-four  hours. 


6  TECHNIC. 

During  this  time,  the  last  should  be  changed  once.  To  in- 
sure perfect  dehydration,  the  specimens,  after  being  drained, 
may  be  placed  in  absolute  alcohol  for  twelve  to  twenty-four 
hours. 

If  the  following  steps  are  not  to  be  carried  out  imme- 
diately the  tissues  shall  be  transferred  to  a  solution  of  70  to 
80  per  cent,  alcohol  in  which  they  may  remain  indefinitely. 

CLEARING. 

After  dehydration  is  completed  the  tissues  are  ready  for 
the  clearing  agents. 

Clearing  is  the  process  by  which  the  alcohol  is  removed 
and  an  agent  that  will  mix  with  the  infiltration  medium  sub- 
stituted. If  paraffin  is  to  be  used,  an  oil  or  fluid  miscible 
with  both  alcohol  and  paraffin  is  necessary;  if  celloidin  in- 
filtration is  to  follow,  then  a  mixture  of  absolute  alcohol 
and  ether  is  used. 

For  the  paraffin  method  the  tissues  are  removed  from  the 
alcohol,  drained  a  few  minutes  and  then  transferred,  usually 
to  an  oil,  for  twenty-four  hours.  The  oil  penetrates  the 
tissues,  removes  the  alcohol,  and  remains  in  its  place. 

CHLOROFORM,  XYLOL,  and  various  oils  may  be  employed, 
among  them  being  turpentine,  which  usually  requires 
twenty-four  hours  for  half-inch  cubes. 

XYLOL  requires  from  six  to  twenty-four  hours,  or  until 
the  tissue  is  transparent. 

CEDAR  OIL  is  used  as  follows:  The  tissues  are  first  placed 
in  a  mixture  of  equal  parts  of  cedar  oil  and  absolute  alcohol 
for  twenty-four  hours.  They  are  then  drained  and  placed 
in  pure  cedar  oil  for  the  same  length  of  time.  If  pure  oil 
alone  is  used,  it  is  changed  several  times  until  the  tissues  are 
transparent,  which  usually  requires  twenty-four  to  forty- 
eight  hours. 


INFILTRATION.  7 

INFILTRATION. 

After  clearing,  the  tissues  are  ready  for  Infiltration. 

Infiltration  is  the  process  by  which  the  interstices  of  the 
tissue  are  filled  with  an  agent  that  hardens  and  allows  the 
tissue  to  be  cut  without  distortion.  There  are  two  impor- 
tant agents,  PARAFFIN  and  CELLOIDIN.  GUM  may  be  used 
for  special  purposes.  The  paraffin  method  will  first  be 
considered. 

After  clearing,  the  tissues  are  drained,  blotted  with  tissue- 
paper,  and  then  placed  in  a  tube  of  melted  paraffin  at  a 
temperature  a  little  above  the  melting-point,  usually  50° 
to  55°  C.  This  is  called  PARAFFIN  No.  i,  and  its  object  is 
the  removal  of  the  bulk  of  the  oil.  After  twelve  to  twenty- 
four  hours  the  tissues  are  removed  to  a  tube  of  fresh  paraffin 
and  allowed  to  remain  the  same  length  of  time.  This  is 
PARAFFIN  No.  2,  and  the  remainder  of  the  oil  is  removed 
and  pure  paraffin  left  in  the  tissues.  The  tissues  are  then 
ready  to  be  BLOCKED. 

By  the  use  of  CHLOROFORM,  infiltration  with  paraffin  can 
be  accomplished,  to  great  extent,  in  the  cold.  The  tissues 
are  completely  dehydrated  with  absolute  alcohol  and  then 
placed  in  PURE  CHLOROFORM  to  replace  the  alcohol.  This  is 
accomplished  when  the  tissues  become  submerged,  usually 
four  to  eight  hours.  They  are  then  transferred  to  a  warm, 
saturated  solution  of  paraffin  in  chloroform,  for  two  to  four 
hours,  and  then  to  pure  melted  paraffin  until  all  the  chloro- 
form has  disappeared  (two  to  twelve  hours). 

If  delicate  structures  are  to  be  infiltrated  they  may  be 
cleared  slowly  by  adding  TOLUOL,  or  BENJOL,  drop  by  drop, 
to  the  specimen  in  absolute  alcohol  and  mixing  after  each 
addition.  By  this  method,  2  c.c.  of  oil  can  be  added  to  the 
same  amount  of  absolute  alcohol  in  four  to  six  hours  and  no 
shrinkage  result.  The  specimens  may  then  be  transferred 


8  TECHNIC. 

to  a  mixture  of  absolute  alcohol  (i  part)  and  toluol  (3  parts) 
for  one  to  three  hours.  They  may  then  be  placed  in  pure 
toluol  from  one  to  four  hours,  the  time  depending  upon  the 
size,  one-eighth  to  one-fourth  inch  in  diameter.  From  this 
it  may  be  transferred  to  a  solution  of  paraffin  in  toluol  for 
two  or  four  hours,  after  which  more  paraffin  is  added,  and 
the  tube  transferred  to  the  paraffin-bath,  where  it  remains 
for  an  hour  or  two,  and  is  then  cast. 

BLOCKING. 

Blocking  may  be  accomplished  by  the  use  of  leaden 
angles,  paper  boxes,  or  wooden  blocks.  The  leaden  angles 
are  of  various  sizes  and  are  used  in  connection  with  brass 
plates.  These  are  all  cooled  in  ice-water,  quickly  dried  and 
the  angles  put  into  place.  A  small  layer  of  paraffin  is  then 
run  into  the  mold,  and  the  tissue  placed  therein,  and 
oriented.  The  mold  is  then  filled  with  melted  paraffin,  and 
as  soon  as  a  scum  is  formed,  the  whole  is  immersed  in  ice- 
water,  and  the  angles  cautiously  removed,  so  that  the 
water  can  act  upon  all  sides  except  the  bottom.  Unless 
this  is  done,  the  paraffin,  in  cooling  rapidly  and  contracting, 
will  enclose  water  bubbles  that  are  unnecessary  and  an- 
noying. A  little  skill  is  required  to  cast  successfully. 
Usually,  by  this  method,  the  paraffin  remains  clear,  a  condi- 
tion much  to  be  desired. 

If  BLOCKS  are  used,  these  should  be  preferably  of  oak,  an 
inch  and  a  quarter  long,  by  seven-eighths  square.  The 
end  is  carefully  and  tightly  wrapped  with  a  strip  of  thin 
paper,  forming  a  cup  one-half  to  one  inch  deep.  The 
specimen  is  then  quickly  oriented  upon  a  thin  layer  of 
paraffin,  and  the  cup  filled  with  paraffin.  It  is  then  set 
aside  and  allowed  to  cool.  The  enclosed  air  bubbles  rise. 
The  paraffin  is  usually  not  clear  by  this  method,  but  is 


BLOCKING.  9 

• 

made  so  by  placing  the  block  for  several  days  upon  paraffin 
bath.  The  warmth  clears  the  paraffin. 

After  casting,  the  blocks  are  trimmed,  and  then  ready 
to  be  cut  with  the  microtome. 

For  the  celloidin  infiltration  method,  FIXATION  and 
DEHYDRATION  are  carried  out  in  the  same  manner  as  for 
paraffin,  but  a  different  clearing  agent  is  used.  A  mixture  of 
equal  parts  of  absolute  alcohol  and  ether  will  clear  tissues  in 
twenty-four  hours,  at  the  end  of  which  time  they  are  ready 
for  the  celloidin. 

CELLOIDIN,  OR  PYROXYLIN,  is  used  in  two  different  solu- 
tions— thick  and  thin.  The  thick  solution  is  prepared  by 
dissolving  one  ounce  of  the  celloidin  in  a  mixture  of  150  c.c. 
each  of  absolute  alcohol  and  ether.  It  is  best  to  soften  the 
celloidin  for  some  hours  in  the  absolute  alcohol,  and  then 
add  the  ether.  Preserve  in  a  magnesium  citrate  bottle. 
The  thin  celloidin  is  made  by  diluting  the  thick  with  an 
equal  part  of  the  alcohol  and  ether  mixture. 

After  clearing,  the  tissues  are  drained  for  a  few  seconds, 
and  then  transferred  to  the  thin  celloidin  for  one  to  four 
days,  and  then  to  the  thick  for  four  to  seven  days.  They 
are  then  ready  to  be  cast. 

The  tissues  may  be  blocked,  as  in  the  paraffin  method,  by 
placing  the  specimen  in  a  paper  cup,  as  above,  upon  a 
wooden,  vulcanite,  composition,  or  glass  block,  and  cover- 
ing with  thick  celloidin.  They  are  then  set  aside  until  a 
thin  scum  forms,  due  to  the  contact  with  the  air,  after 
which  they  are  placed  in  80  per  cent,  alcohol  to  harden 
the  celloidin.  In  twenty-four  to  forty-eight  hours  they  are 
ready  to  cut. 

Another  way  to  cast  is  to  place  the  tissues  in  low  Stender 
dishes,  cover  well  with  very  thick  celloidin,  and  orient 
immediately.  When  a  scum  has  formed,  the  dishes  are 
lowered  into  another  containing  the  alcohol  for  hardening. 


10  TECHNIC. 

Still  another  way  is  to  place  the  tissues  with  thick  celloi- 
din in  stoppered  paraffin  tubes,  and,  after  several  days, 
loosen  the  stopper  and  allow  the  alcohol  and  ether  to  gradu- 
ally escape.  When  the  celloidin  has  retracted  from  the 
sides,  the  mold  is  lifted  out  and  placed  in  the  alcohol. 

If  the  celloidin  is  not  hard  enough,  the  blocks  may  be 
placed,  for  twenty-four  to  forty-eight  hours,  in  eighty  per 
cent,  alcohol,  containing  i  to  5  per  cent,  glycerin. 

The  blocks  may  be  hardened  without  the  use  of  alcohol 
by  placing  them  in  chloroform  vapor  or  pure  chloroform 
until  solid. 

Gum. — This  infiltration  medium  is  prepared  as  follows: 

Syrup  ^  Cane  Sugat 2 8.  5  gms. 

\  Water      30  c.c. 

P         (  Gum  Acacia 57  gms. 

\  Water 310  c.c. 

Mix  together  four  parts  of  the  syrup,  five  parts  of  the  gum 
and  to  this  add  nine  parts  of  a  saturated  solution  of  boric 
acid.  Filter  through  muslin. 

The  tissues  are  thoroughly  washed  free  of  any  trace  of 
alcohol,  and  are  then  placed  in  the  above  solution,  and  al- 
lowed to  remain  until  penetrated,  which  requires  at  least 
twenty-four  hours  if  half-inch  cubes  are  used.  A  longer 
time  is  better.  The  process  is  aided  by  allowing  the  jar 
with  the  tissues  to  stand  in  a  warm  place. 

Tissues  infiltrated  with  gum  must  be  frozen  and  cut  in  a 
freezing  microtome. 

After  the  above  steps  have  been  finished,  the  tissues  are 
ready  to  be  sectioned. 

Paraffin  blocks  are  cut  dry,  the  knife  of  the  microtome 
being  placed  so  that  it  meets  the  block  squarely.  When 
large  objects  are  cut,  it  is  some  imes  necessary  to  place  the 


DECALCIFICATION.  1 1 

• 

knife  obliquely.  Very  thin  sections  may  be  straightened 
for  mounting  by  floating  them  in  warm  water.  The  slide 
prepared  with  Mayer's  albumen  (see  p.  28)  is  then  dipped 
beneath  them,  and  if  carefully  lifted,  the  section  rests 
smoothly  in  place  thereon. 

Celloidin  blocks  are  treated  differently.  The  knife  is 
placed  obliquely  and  kept  moist  with  80  per  cent,  alcohol. 
The  block  likewise' is  kept  moist,  and  as  the  sections  are  cut, 
they  are  transferred,  by  means  of  a  large  sable  brush,  to  a 
dish  of  the  same  alcohol,  and  allowed  to  remain  there  until 
required.  If  the  celloidin  is  too  soft,  the  sections  will  be 
quite  thick.  This  may  be  remedied  by  hardening  the 
blocks  in  alcohol  containing  i  to  5  per  cent,  of  glycerin. 
Celloidin  answers  very  well  for  the  nerve  system,  but 
where  thin  sections  are  desired,  the  paraffin  method  is 
preferable. 

DECALCIFICATION. 

BONE  AND  TEETH  may  be  ground  for  study.  If  sections 
are  desired,  the  inorganic  matter  must  be  removed  by 
means  of  acids.  This  process  is  Decalcification. 

Whole  teeth  and  small  pieces  of  bone  are  fixed  and  hard- 
ened in  solutions  containing  a  salt  of  chromium,  and  are 
allowed  to  remain  as  long  as  required.  After  being  thor- 
oughly washed  and  dehydrated  as  above,  they  are  ready 
for  the  decalcifying  agent,  of  which  large  quantities  are 
to  be  used.  The  solutions  given  below  are  the  most 
important. 

i.  Phloroglucin -nitric  acid  is  no  doubt  the  best.  It 
consists  of 

Phloroglucin        i  gm. 

Nitric  acid  (concentrated)    ....         5  c.c. 
Alcohol  (70  per  cent.) 100  c.c. 


1 2  TECHNIC. 

The  phloroglucin  is  dissolved  in  the  nitric  acid,  and  al- 
lowed to  stand  until  the  fumes  have  disappeared  (about 
twenty-four  hours).  The  alcohol  is  then  added,  and  the 
solution  is  ready  for  use.  The  teeth  or  bone  are  placed 
therein  until  readily  penetrated  by  a  needle  or  cut  with  a 
scalpel.  The  tissues  are  then  transferred  to  alcohol  and 
dehydrated  in  the  manner  already  stated.  Celloidin  is  the 
better  infiltrating  agent,  as  heat  tends  to  harden  osseous 
tissues.  Additional  nitric  acid  may  be  added  if  desired, 
but  not  over  20  per  cent. 

Mayer's  Solution  is  a  5  per  cent,  solution  of  nitric  acid 
in  95  per  cent,  alcohol.  It  acts  very  well.  The  alcohol  is 
supposed  to  prevent  swelling  of  the  tissues. 

Trichloracetic  Acid. — A  5  per  cent,  solution  of  this  is 
used.  It  is  slower  than  the  nitric  acid,  but  the  treatment 
is  the  same. 

STAINING. 

In  order  to  study  the  various  portions  of  a  cell,  they 
must  be  differently  stained.  There  are  three  classes  of 
stains;  i,  Nuclear,  2,  Protoplasmic,  and  3,  Special;  of  these 
two  are  generally  used — NUCLEAR,  or  BASIC;  and  PROTO- 
PLASMIC, or  ACID.  The  NUCLEAR  stain  is  used  first,  followed 
by  the  PROTOPLASMIC  STAIN;  this  is  called  counter-staining. 
Gruebler's  products  are  recommended. 

i.  Nuclear  Stains. — The  most  important  of  the  basic 
stains  are  HEMATOXYLIN  and  the  ANILIN  DYES. 

There  are  several  ways  to  prepare  the  hematoxylin. 
The  most  rapid  is  the  HARRIS  METHOD. 

HEMATOXYLIN  (HARRIS). 

Hematoxylin      i  gm. 

Absolute  alcohol 10  c.c. 

Potassium  alum  (sat.  aq.  sol.)     .    .     200  c.c. 


STAINING.  13 

Dissolve  the  hematoxylin  in  the  alcohol  and  add  if  fo  the 
alum  solution.  When  this  is  brought  to  a  boil,  add  i  gm. 
of  mercuric  oxid,  and  cool  the  solution  rapidly.  The 
oxygen  liberated  ripens  the  solution  immediately,  and  the 
stain  is  ready  for  use  when  cool.  It  should  be  filtered  and 
diluted  with  three  to  four  times  the  quantity  of  water,  when 
ready,  and  will  require  three  to  five  minutes  to  stain. 

DELAFIELD'S  HE'MATOXYLIN  is  prepared  as  follows : 

Hematoxylin 4  gms. 

Alcohol 25  c.c. 

Ammonium  alum  (sat.  aq.  sol.)       .     400  c.c. 

Dissolve  the  hematoxylin  in  the  alcohol,  and  add  this 
solution,  drop  by  drop,  to  the  alum  solution.  Expose  this 
to  the  light  and  air  for  a  week  or  more,  and  then  filter.  To 
the  filtrate  add 

Glycerin       100  c.c. 

Methyl  alcohol       100  c.c. 

Expose  again  for  a  long  time,  and  filter.  This  solution 
must  be  diluted  three  to  four  times,  like  Harris*. 

ACID  HEMATOXYLIN  is  made  up  as  follows : 

Hematoxylin      i  gm. 

Absolute  alcohol 30  c.c. 

Glycerin       60  c.c.  \  Saturated 

Water      60  c.c.  /  with  alum. 

Glacial  acetic  acid 3  c.c. 

Add  the  glycerin  and  water  to  the  hematoxylin,  dis- 
solved in  the  alcohol;  then  add  the  acid.  This  solution 
must  be  exposed  to  the  light  for  three  weeks,  when  it  be- 
comes bluish.  Sections  stained  in  it  are  at  first  not  dark, 
but  when  exposed  to  the  light,  they  become  bluish. 

Most  of  the  ANILIN  DYES  are  not  stable,  but  fade  when  ex- 
posed to  the  light. 


14  TECHNIC. 

METHYLENE  BLUE  is  used  in  connection  with  the  nerve 
system. 

METHYL  GREEN  is  used  for  organs  and  tissues  containing 
mucin,  and  in  blood  stains. 

SAFRANIN  is  used  for  the  study  of  karyokinesis.  It 
should  be  used  upon  tissues  hardened  in  Flemming's 
solution. 

Safranin       i  gm. 

Absolute  alcohol 100  c.c. 

Water 200  c.c. 

Sections  may  remain  in  this  solution  from  two  to  twenty- 
four  hours  and  even  longer.  They  are  then  washed  in 
plain  alcohol  or  carefully  differentiated  in  acid  alcohol,  and 
then  only  the  chromatin  retains  the  stain. 

BISMARCK  BROWN. — This  stain  is  not  very  soluble  in 
water.  A  saturated  solution  is  made  by  boiling  the  stain  in 
water,  and  then  filtering.  This  gives  a  3  to  4  per  cent, 
solution,  which  is  diluted  by  adding  one-third  volume  of 
absolute  alcohol.  This  stains  rapidly,  but  does  not  over- 
stain.  It  is  used  to  advantage  in  contrast  with  hematoxy- 
lin,  in  connective  tissues  and  cerebellum.  It  answers  well 
in  staining  the  acid  cells  of  the  stomach.  The  sections 
should  first  be  deeply  stained  with  hematoxylin,  and  then 
subjected,  five  minutes,  to  the  above  stain.  The  acid 
cells  are  distinctly  brown,  while  the  peptic  cells  have  a 
bluish  cast. 

2.  Protoplasmic  Stains. — The  more  common  acid  stains  are 

EOSIN,  PICRIC  ACID,  VAN  GlESON  and  ORANGE. 

Eosin  is  commonly  used  as  a  1/2/01  per  cent,  aqueous 
or  alcoholic  solution.  It  requires  one  to  two  minutes, 
and  should  be  washed  off  with  water,  if  an  aqueous  solution 
has  been  used;  otherwise  with  alcohol. 

PICRIC  ACID. — A  saturated  aqueous  solution  is  used  for 


STAINING.  IS 

15  to  30  seconds.     It  is  then  washed  quickly  with  ^5  per 
cent,  alcohol. 

VAN  GIBSON  consists  of  PICRIC  ACID  and  ACID  FUCHSIN. 

Picric  acid  (sat.  aq.  sol.)     ....     100  c.c. 
Acid  fuchsin  (i  per  cent,  sol.)      .    .       5  c.c. 

Stain  from  one  to  three  minutes,  and  wash  with  alcohol. 
A  little  stronger  solution  is  used  for  the  nerve  system. 

ORANGE  is  used  as  a  i  per  cent,  solution,  and  is  em- 
ployed as  a  blood  stain. 

There  are  stains  that  affect  both  nucleus  and  protoplasm 
sufficiently  to  differentiate  each  well.  Such  are  CARMIN 
and  CARMINIC  ACID  COMBINATIONS.  They  are  used  chiefly 
in  BULK  STAINING,  especially  for  entire  embryos. 

BORAX  CARMIN  consists  of  CARMIN  boiled  in  a  SOLUTION 
OF  BORAX. 

Carmin 2  gms. 

Borax  (2  per  cent.  aq.  sol.)      .    .    .     200  c.c. 

Boil,  and  then  add  a  few  drops  of  a  5  per  cent,  solution 
of  acetic  acid  and  100  c.c.  of  70  per  cent,  alcohol.  After  a 
few  hours  filter,  and  to  the  filtrate  add  a  small  piece  of 
thymol  or  menthol,  to  preserve. 

Allow  the  solution  to  stain  sections  for  15  to  20  minutes, 
and  then  differentiate  with  acid  alcohol  prepared  as 
follows : 

Hydrochloric  acid  (concentrated)   .         i  c.c. 

Water      29  c.c. 

Alcohol  (95  per  cent.)       70  c.c. 

This  stain  is  also  used  for  bulk  staining. 

ALUM     CARMIN. — This    is     prepared    by     boiling     ONE 

GRAM    OF    CARMIN    with    IOO    C.C.    OF    A  5    PER    CENT.    SOLU- 
TION OF  AMMONIUM  ALUM.     This  is  filtered  when  cool,  and 


1 6  TECHNIC. 

preserved  as  above.     It  also  requires  the  same  time  for 
staining. 

PICRO-CARMIN  is  a  DOUBLE  STAIN,  and  its  preparation 
is  not  so  simple.  It  consists  of  the  following: 

Carmin 4  gms. 

Ammonia  (concentrated)  ....  10  c.c. 
Water 200  c.c. 

Dissolve  the  carmin  in  the  ammonia,  to  which  a  little 
water  has  been  added.  Then  add  the  water,  and,  after 
24  hours,  filter.  Allow  the  solution  to  stand  until  most  of 
the  ammonia  has  evaporated  and  add  an  aqueous  saturated 
solution  of  picric  acid  until  precipitation  occurs.  The 
solution  must  be  stirred  all  the  time.  Set  it  aside  to 
crystallize  and  to  evaporate  to  one-third  of  its  bulk.  Pour 
off  the  liquid  and  evaporate  it  to  dryness.  Dissolve  the 
first  crystals  and  evaporate  to  dryness.  This  residue,  as 
a  i  per  cent,  solution  in  water,  is  a  very  good  double  stain. 

PARACARMIN    consists    of    CARMINIC    ACID,    ALUMINUM 

CHLORID,  CALCIUM  CHLORID  and  70  PER  CENT.  ALCOHOL. 

Carminic  acid i       gm. 

Aluminum  chlorid 0.5  gm. 

Calcium  chlorid 4       gms. 

Alcohol  (70  per  cent.) 100       c.c. 

Dissolve  and  filter. 

This  stain  is  especially  useful  in  EMBRYOLOGY,  as  it  does 
not  overstain,  and  may  be  used  again  and  again.  On 
sections,  it  is  a  good  contrast  stain  to  Weigert's  elastica 
stain. 

EHRLICH-BIONDI-HEIDENHAIN  STAIN. — This  stain  is  used 
especially  in  blood  work  or  those  tissues  containing  many 
leukocytes.  It  is  composed  of: 

Orange  (saturated  aq.  sol.)  .  .  .  100  c.c. 
Acid  fuchsin  (saturated  aq.  sol.)  .  20  c.c. 
Methyl  green  (saturated  aq.  sol.)  .  50  c.c. 


STAINING.  17 

This  solution  is  diluted  to  make  a  solution  of  i-ioo,"  \vhich, 
upon  the  addition  of  acetic  acid,  must  be  bright  red.  It  is 
difficult  to  prepare,  and  so  is  better  bought  ready  for  use. 

Organs  should  be  fixed  in  corrosive  sublimate,  and  sections 
stained  for  12  to  24  hours,  washed  with  90  per  cent,  alcohol, 
and  dehydrated  with  absolute  alcohol,  cleared  and  mounted 
in  balsam. 

3.  Special  Stains. — These  are  used  to  bring  out  special 
structures  or  tissues.  Among  these  the  most  important 
are  the  Gold,  Silver,  Myelin  and  Elastica  Stains,  Osmic 
Acid,  Sudan  III,  and  van  Gieson's  Stains. 

The  Gold  Stain,  used  for  lymphatic  spaces  and  nerve  end- 
ings, is  not  always  successful;  but  when  it  succeeds,  the 
results  are  beautiful  and  gratifying.  There  are  a  number 
of  ways  of  preparing  the  solution,  but  the  best  is  the  boiling 
method. 

Eight  c.c.  of  a  i  per  cent,  solution  of  gold  chlorid  are 
mixed  with  2  c.c.  of  formic  acid,  and  brought  to  a  boil, 
and  cooled.  This  is  repeated  three  times,  and  it  is  then 
ready  for  use.  Small  strips  (3  to  5  mm.  thick)  are  placed 
in  it  for  one  hour,  and  the  container  kept  in  the  dark. 
They  are  then  washed  in  distilled  water,  and  exposed 
to  the  light  in  a  solution  of  formic  acid  (10  c.c.  of  acid  to 
40  c.c.  of  water)  for  one  or  two  days.  They  are  then 
dehydrated  in  70  per  cent,  alcohol,  and  left  there  for  4  to  8 
days  or  longer. 

Silver  Nitrate. — Pieces  of  the  nerve  system  are  fixed  in 
the  Golgi  solution  (see  Fixatives,  p.  4)  and  then  placed  in 
silver  nitrate. 

Cajal-Golgi  Method. — Thin  pieces  of  nerve  tissue  are 
placed  in  the  following  solution  and  hardened  for  three 
days: 

i.           Potassium  bichromate  solution  (2  to  2.5%)   8  parts. 
Osmic  acid  solution  (i%) 2  parts. 


1 8  TECHNIC. 

2.  Transfer  tissues  to  a  solution  of  silver  nitrate  of  1/2 
to  3/4  per  cent,  strength.     First  blot  off   the  bichromate 
solution   and    then   rinse   tissues   thoroughly  in    the   some 
silver  solution.     Then  place  tissues  in  at  least  thirty  times 
their  volume  of  silver  solution  and  allow  them  to  stand  in 
the  dark  for  three  days.     Change  the  silver  solution  after 
the  first  eight  to  twelve  hours. 

3.  Return  to  the  following  solution  for  one  to  two  days: 

Potassium  bichromate  solution  (2%)  20  parts 
Osmic  acid  solution  (i%) 2  parts 

4.  Wash  quickly  with  distilled  water  and  return  to  a 
fresh   solution   of  silver  nitrate  of  previous   strength   for 
thirty-six  to  forty-eight  hours. 

5.  Dehydrate  in  twenty  times  the  bulk  of  95  per  cent, 
alcohol  for  twenty  minutes;  the  alcohol  should  be  renewed 
after  the  first  five  minutes. 

6.  Dehydrate  in  same  bulk  of  absolute  alcohol  for  thirty 
minutes;  renew  after  ten  minutes. 

7.  Replace  alcohol  by  same  volume  of  absolute  alcohol 
and  ether  (equal  parts)  for  twenty  minutes. 

8.  Transfer  to  thin  celloidin  for  twenty-five  minutes  and 
then  thick  celloidin  for  ten  minutes. 

9.  Block  and  harden  in  chloroform  for  about  ten  minutes. 

10.  Place  for   thirty  minutes  in   the  following  clearing 
solution : 

Carbolic  acid  (melted)       50  c.c. 

Oil  of  thyme  or  cedar        50  c.c. 

Oil  of  bergamot          25  c.c. 

11.  Section,  keeping  knife  and  block  moist  with  above 
clearing  fluid. 

12.  Mount  on  slides,  remove  clearing  fluid  by  means  of 
xylol,    blot,    cover   with    thick   balsam,    but   do   not   use   a 
cover-glass. 


STAINING.  19 

This  method  gives  excellent  results. 

Silver  nitrate  is  used  chiefly  for  nerve  tissues.  It  may 
also  be  injected  into  the  blood-vessels  to  stain  the  en- 
dothelium,  and  into  the  lymphatics  to  outline  the  small  chan- 
nels. It  has  also  been  used  in  the  liver  to  outline  the  bile 
capillaries. 

Myelin  Stain. — This  is  WEIGERT'S  HEMATOXYLIN  STAIN 
FOR  MYELIN  SHEATHS.  The  tissues  are  fixed  in  bichromate, 
though  this  is  not  absolutely  necessary.  Results  are 
more  certain  if  the  tissues  have  been  fixed  in  a  bichromate 
solution,  as  they  respond  more  readily  to  the  stains  and  are 
not  so  likely  to  fade.  Celloidin  infiltration  is  usually  the  best. 

After  the  sections  have  been  cut,  they  are  placed,  for 
four  to  twenty-four  hours,  in  the  following  solution: 

Potassium  bichromate       5  gms. 

Chrom  alum        2  gms. 

Water      100  c.c. 

They  are  then  washed  thoroughly,  and  transferred  to  the 
following  solution  for  twenty-four  hours: 

Copper  acetate       5       gms. 

Acetic  acid  (36  per  cent.)     ....         5       c.c. 

Chrom  alum          2.5  gms 

Water 100       c.c. 

Add  the  chrom  alum  to  the  water,  bring  to  a  boil,  remove 
the  heat,  add  the  acetic  acid,  and  then  the  copper  acetate, 
stirring  thoroughly  until  the  last  of  the  salt  is  dissolved. 
When  cold  the  solution  should  be  clear. 

This  solution  is  a  mordant.  The  sections  are  carefully 
washed  and  carried  into  the  following  solution: 

Hematoxylin       i  gm. 

Absolute  alcohol 10  c.c. 

Lithium    arbonate  (sat.  aq.  sol.)    .  i  c.c. 

Water 90  c.c. 


20  TECHNIC. 

The  sections  are  stained  from  fifteen  minutes  to  two  or 
four  hours  in  this  solution,  and  then  washed  until  the 
washings  are  clear.  They  are  then  differentiated  in  the 
following: 

Potassium  ferricyanid       5  gms 

Borax  (if  granular,  use  one-half  amount)      4  gms. 
Water       200  c.c. 

In  this  solution  they  must  remain  until  the  gray  matter 
becomes  yellowish.  This  change  must  be  watched  under 
the  microscope.  The  sections  are  immediately  transferred 
to  water,  which  is  frequently  renewed.  They  are  then 
dehydrated,  cleared  and  mounted  in  balsam. 

The  myelin  sheaths  will  be  bluish-black. 

Weigert-Pal  Method. — i.  Fix  as  for  Weigert  method  and 
after  cutting  place  the  sections  in  a  1/2  per  cent,  solu- 
tion of  chromic  acid  for  several  hours.  This  step  is  not 
necessary  if  a  chromium  salt  has  previously  been  used  for 
fixation. 

2.  Wash  and   transfer  to  the  hematoxylin  solution  for 
twenty-four  to  forty-eight  hours. 

3.  Wash  with    water   containing   about  2  per   cent,  of 
lithium  carbonate.     The  sections  should  be  bluish. 

4.  Differentiate  in  a  1/4  per  cent,   aqueous  solution  of 
potassium  permanganate  until  the  gray  substance  of  the 
nerve  tissue  is  yellowish-brown  in  color. 

5.  Transfer   to   the  following    solution    until    the    gray 
substance  is  almost  colorless : 

Potassium  sulphit i  part. 

Oxali    acid i  part. 

Distilled  water       200  parts. 

This  solution  requires  but  a  few  seconds  to  produce  its 
action. 


STAINING.  21 

6.  Wash  thoroughly  with  water,  dehydrate,  clear  and 
mount. 

By  this  method  all  the  tissues,  except  the  myelin 
sheaths,  are  decolorized. 

Weigert's  elastica  stain  is  used  to  demonstrate  the 
ELASTIC  TISSUE  in  organs  and  tissues,  and  is  prepared  as 
follows : 

Fuchsin        2  gms. 

Resorcin 4  gms. 

Water 200  c.c. 

This  mixture  is  brought  to  a  boil,  and  then  25  c.c.  of  a 
solution  of  liquor  ferri  sesquichlorati  added,  the  mixture 
stirred  and  boiled  for  3  to  5  minutes.  When  cool,  it  is 
filtered,  and  the  precipitate  dissolved  upon  the  filter,  in 
200  c.c.  of  95  per  cent,  alcohol.  This  is  stirred  and  boiled 
until  the  precipitate  is  entirely  dissolved.  The  solution  is 
then  cooled  and  brought  up  to  200  c.c.  with  95  per  cent, 
alcohol  and  4  c.c.  of  hydrochloric  acid  added. 

Carbolic  acid  in  the  same  proportion  may  be  used  in 
place  of  the  resorcin. 

Sections  should  be  stained,  from  20  minutes  to  an  hour, 
in  this  solution,  wash  well  in  95  per  cent,  alcohol,  cleared 
and  mounted. 

Osmic  Acid. — This  is  used  as  a  i  per  cent,  solution  as  a 
special  stain  for  fat,  which  it  turns  black  and  renders 
almost  insoluble  in  the  ordinary  reagents  used  in  technic. 

Sudan  III. — A  solution  of  this  stain  is  also  a  special 
stain  for  fat,  coloring  it  a  deep  red. 

Van  Gieson's  Stain. — Although  this  may  be  classed  under 
the  protoplasmic  stains,  it  is,  nevertheless,  a  special  stain  for 
white  fibrous  connective  tissue.  This  it  stains  a  beautiful 
rose-red,  while  the  other  tissues  are  stained  yellowish  to 
brown. 


22  TECHNIC. 

CLEARING  AGENTS  FOR  SECTIONS. 

After  staining  and  dehydrating,  the  sections  are  to  be 
CLEARED  (see  Slide  Technic,  p.  30).  The  CLEARING  AGENT 
removes  the  alcohol  and  prepares  the  section  for  the  final 
step  of  mounting.  These  agents  differ  from  those  used 
in  block  technic.  When  balsam  or  dammar  is  to  be  used, 
the  sections  are  cleared  with  an  OIL.  Of  these,  the  follow- 
ing are  the  most  important: 

CREOSOTE  (BEECHWOOD)  is  one  of  the  commonest  and  the 
best  for  general  laboratory  use. 

OIL  OF  ORIGANUM  is  also  a  very  useful  clearing  agent,  and 
is  especially  adapted  for  celloidin  sections  and  those  stained 
with  van  Gieson's  stain.  It  neither  dissolves  the  celloidin 
nor  renders  it  stiff. 

OIL  OF  CLOVES  acts  rapidly,  but  dissolves  celloidin  and 
removes  anilin  dyes.  It  does  not  evaporate,  but  renders 
the  section  hard  and  sections  become  yellow  with  age. 

CEDAR-WOOD  OIL  clears  slowly,  but  has  the  advantage  of 
not  abstracting  the  anilin  dyes. 

OIL  OF  BERGAMOT  is  very  good,  but  has  the  disadvantage 
of  removing  eosin. 

XYLOL,  TOLUOL,  BENZOL,  all  act  very  rapidly,  and  re- 
quire dehydration  with  absolute  alcohol.  They  are  useful 
with  anilin  stains,  and  are  readily  applicable  as  solvents  of 
balsam.  They,  however,  render  celloidin  stiff  and  hard. 

CARBOL- XYLOL  is  a  mixture  of  XYLOL  and  CARBOLIC  ACID. 

Xylol        3  parts. 

Carbolic  acid       i  part. 

For  larger  sections,  i.  e.,  brain  stem,  the  writer  prefers  the 
following  mixture: 

Carbol-xylol        2  parts. 

Clove  oil i  to  2  parts. 


CLEARING   AGENTS.  23 

The  clove  oil  keeps  the  celloidin  soft  and  pliable  so  that 
upon  blotting  the  sections  are  flat  and  not  raised  in  ridges. 

It  acts  very  rapidly,  and  is  best  for  hematoxylin  and 
carmin  stains;  it  does  not  stiffen  celloidin. 

ANILIN  OIL-XYLOL  consists  of  ANILIN  OIL,  two  parts,  and 
XYLOL,  one  part.  It  is  more  commonly  used  than  the 
preceding. 

Most  of  the  oils  require  about  five  minutes  to  act.  The 
sections  are  set  aside  during  this  time.  In  the  case  of 
rapidly  acting  agents,  the  slides  are  retained  in  the  hand  and 
rocked  back  and  forth  until  the  section  is  clear.  This  is 
usually  accomplished  in  a  minute  or  so. 

After  clearing,  the  sections  are  ready  for  the  final  step, 
that  of  MOUNTING.  There  are  a  number  of  MOUNTING 

MEDIA,  SUCh  as  BALSAM,  DAMMAR,  FARRANT'S  SOLUTION    and 
GLYCERIN  JELLY. 

BALSAM. — Sections  to  be  mounted  in  balsam  must  be 
thoroughly  dehydrated  and  cleared  in  an  oil.  The  oil  is 
then  removed  by  blotting,  a  small  drop  of  balsam  placed 
upon  the  specimen  and  a  clean  cover-glass  applied. 

The  balsam  is  soluble  in  chloroform,  turpentine,  benzol  or 
xylol.  The  latter  agent  is  the  best.  Sections  mounted  in 
this  medium  are  permanent. 

Dammar  is  more  complex.     It  consists  of  the  following: 

Gum  dammar ij  oz. 

Gum  mastic J  oz. 

Turpentine 2     oz. 

Chloroform 2     oz. 

The  dammar  is  to  be  dissolved  in  the  turpentine,  and  the 
mastic  in  the  chloroform.  Each  is  to  be  filtered,  the 
filtrates  mixed  and  the  mixture  filtered.  This  is  to  be  kept 
in  a  well-stoppered  bottle  to  prevent  the  evaporation 
of  the  chloroform. 


24  TECHNIC. 

FARRANT'S  SOLUTION. — Sections  to  be  mounted  in  this 
medium  are  neither  dehydrated  nor  cleared,  but  washed 
with  water  and  mounted  in  this  solution.  It  is  prepared 
by  adding  gum-arabic  to  a  mixture  of  equal  parts  of  water, 
glycerin  and  a  saturated  solution  of  arsenious  acid.  The 
solution  must  be  filtered  after  the  gum  is  dissolved,  and 
should  have  the  consistence  of  a  thick  syrup. 

Preparations  mounted  in  this  medium  may  be  made 
permanent  by  ringing.  This  is  done  by  running  a  ring  of 
cement  around  the  edge  of  the  cover-glass. 

Glycerin  Jelly. — This  medium  must  be  warmed  before  it 
can  be  used.  A  drop  is  placed  upon  the  specimen,  and  the 
cover-glass  quickly  applied,  as  this  medium  sets  rapidly.  It 
is  used  for  special  purposes,  as  for  isolated  cells,  urinary 
casts,  crystals,  etc.  Neither  dehydration  nor  clearing  is 
necessary. 

INJECTION. 

INJECTION  MASSES. — In  order  to  study  the  circulatory 
system,  the  vessels  must  be  injected  with  a  substance  that 
will  outline  them.  For  this  purpose,  either  an  aqueous  solu- 
tion of  carmin  or  of  Berlin  blue,  or  gelatin  masses  are  used. 

BERLIN  BLUE  is  used  in  water,  one  part  to  20,  and  this  is 
injected  with  a  hand  syringe  or  by  continuous  air  pressure. 
It  gives  very  good  results. 

The  GELATIN  MASSES  may  be  either  CARMIN  or  PRUSSIAN 
BLUE. 

The  CARMIN  MASS  consists  of  the  following: 

Carmin 2  gms. 

Water. 
Ammonia. 

Stir  the  carmin  in  a  little  water,  and  add  strong  ammonia, 
drop  by  drop,  until  the  carmin  is  entirely  dissolved.  Filter 


INJECTION.  25 

the  solution  and  add  it  carefully  to  the  melted  gelatin. 
The  latter  is  prepared  by  soaking  gelatin  in  double  its 
quantity  of  water,  and  melting.  The  mixture  is  stirred 
and  then  neutralized  with  dilute  acetic  acid.  If  too  acid, 
the  carmin  will  be  precipitated,  and  if  the  ammonia  is  not 
neutralized  and  the  gelatin  is  quite  alkaline,  the  stain  will 
not  be  limited  to  the  injected  vessels,  but  will  be  diffused 
into  the  surrounding  tissues. 

This  mass  should  be  filtered  while  hot,  and  preserved 
with  a  little  camphor. 

The  PRUSSIAN  BLUE  MASS  is  somewhat  similar.  Four 
gms.  of  the  Prussian  blue  are  stirred  into  80  c.c.  of  water, 
and  the  mixture  added  to  gelatin  prepared  as  above.  The 
solution  is  filtered  while  hot,  and  preserved  with  camphor, 
or  covered  with  methyl  alcohol. 

The  entire  body,  or  individual  organs,  may  be  injected. 
When  the  hand  syringe  is  used,  great  care  must  be  exercised 
that  the  pressure  be  not  too  great,  as  the  vessels  will  rupture 
and  the  mass  extravasate.  The  continuous  air  pressure 
method  is  the  better.  The  mass  must  be  melted  and  the 
animal  kept  warm  by  immersion  in  warm  water.  As  soon 
as  the  injection  is  complete,  the  animal  or  organ  is  im- 
mersed in  ice- water,  so  that  the  gelatin  may  set  immediately. 
When  the  body  is  cooled,  the  organs  are  cut  into  blocks, 
and  transferred  to  80  per  cent,  alcohol,  where  they  remain 
until  thoroughly  hardened,  which  takes  from  one  to  three 
days.  They  are  then  treated  with  95  per  cent,  alcohol  to 
dehydrate,  cleared  and  infiltrated  like  any  other  tissue. 

Blood  is  drawn  from  the  finger  tip  or  lobe  of  the  ear.  The 
part  is  thoroughly  cleansed  and  finally  washed  with  alcohol. 
A  sterilized  needle  is  then  plunged  to  a  depth  of  about  one- 
eighth  of  an  inch,  and  the  blood  allowed  to  flow.  The  part 
should  not  be  squeezed,  as  this  dilutes  the  blood  with  lymph, 
and  causes  errors  in  accurate  work. 


26  TECHNIC. 

BLOOD  SPREADS  are  obtained  by  touching  a  drop  of 
blood  with  a  cover-glass,  and  immediately  placing  this 
upon  a  second  glass.  The  two  are  then  slid  apart,  so  that  a 
thin  film  of  blood  is  present  upon  each.  If  the  glasses  are 
lifted  apart,  the  cells  are  greatly  distorted  and  useless  for 
study.  The  spreads  are  allowed  to  dry  in  the  air,  and  then 
fixed  by  (i)  HEAT,  (2)  the  ABSOLUTE  ALCOHOL-FORMALIN 

SOLUTION,  Or  (3)  ABSOLUTE  ALCOHOL-ETHER  MIXTURE. 

If  HEAT  is  used,  the  spreads  are  placed  in  an  oven,  and 
kept  at  a  temperature  of  120°  C.  for  twenty  minutes. 
Ehrlich  prefers  this  method. 

The  ALCOHOL-ETHER  MIXTURE  consists  of  equal  parts  of 
absolute  alcohol  and  ether.  This  fixes  the  spreads  in  twenty 
minutes.  Results  with  this  fixative  are  very  good. 

The  ALCOHOL-FORMALIN  MIXTURE  consists  of  nine  parts 
of  absolute  alcohol  and  one  part  of  formalin.  Spreads  are 
fixed  in  twenty  minutes. 

After  fixation,  the  spreads  are  allowed  to  dry,  and  may 
then  be  stained  like  any  other  tissue.  Hematoxylin  and 
eosin  give  a  good  result. 

Among  special  stains  is  the  EHRLICH-BIONDI-HEIDENHAIN 
STAIN.  For  its  composition,  see  Stains,  p.  16. 

WRIGHT'S  BLOOD  STAIN  is  one  of  the  most  satisfactory, 
and  is  prepared  in  the  following  manner : 

Steam  1.5  grams  of  methylene  blue  in  150  c.c.  of  a  i  per 
cent,  aqueous  solution  of  sodium  bicarbonate  for  one  hour, 
in  a  sterilizer.  Add  a  i/io  per  cent,  aqueous  solution 
of  yellowish  eosin  to  100  c.c.  of  the  methylene  blue  solution 
until  the  mixture  turns  purple,  and  a  yellowish  metallic 
scum  forms  upon  the  surface,  and  a  blackish  precipitate 
appears;  about  500  c.c.  of  eosin  solution  will  be  required, 
and  it  should  be  added  slowly,  while  constantly  stirring. 
The  solution  is  then  filtered,  the  precipitate  dried  and  made 
into  a  saturated  solution  with  methyl  alcohol.  This  solu- 


BLOOD.  27 

• 

tion  is  filtered  and  80  c.c.  of  the  filtrate  are  diluted  with 
20  c.c.  of  methyl  alcohol. 

Dried  spreads  are  stained  for  one  minute  with  this  solu- 
tion, and  the  stain  then  diluted  upon  the  glass,  with  water, 
until  the  stain  is  semi-transparent.  After  two  or  three 
minutes,  the  spreads  are  thoroughly  washed  with  distilled 
water,  dried  quickly  and  mounted.  The  acidophilic 
granules  are  reddish-lilac  and  red,  while  the  basophilic 
granules  are  deep  blue  or  even  black. 

This  solution  both  fixes  and  stains  the  cells. 

LEISCHMAN'S  STAIN  is  a  modification  of  Wright's.  It 
can  be  purchased  in  solid  form  and  is  very  satisfactory. 

EOSIN  and  METHYLENE  BLUE  give  good  results.  The 
spreads  are  stained  in  a  1/2  per  cent,  alcoholic  solution 
of  eosin  for  two  or  three  minutes,  using  gentle  heat.  Then 
they  are  placed  in  a  saturated  aqueous  solution  of  methylene 
blue  for  two  or  three  minutes.  The  spreads  are  then 
thoroughly  washed,  dried  and  mounted  in  balsam.  As  a 
rule,  the  granules  of  the  leukocytes  are  well -stained. 

In  order  to  obtain  the  bell-shaped  red  cells,  the  finger 
should  be  thoroughly  cleansed,  and  the  blood  drawn  as 
usual.  The  first  drop  should  be  wiped  off  and  a  drop  of  i 
per  cent,  osmic  acid  solution  placed  over  the  puncture. 
The  blood  then  flows  into  the  osmic  acid,  which  acts  as  a 
fixative,  and  prevents  contact  with  the  air  until  fixation 
is  complete.  If  this  drop  be  examined  under  the  micro- 
scope, the  bell-shaped  cells  will  be  seen  in  great  numbers. 

BLOOD  PLATELETS  may  also  be  stained  in  the  above  way. 

ERYTHROBLASTS  of  the  spleen  may  be  studied  in  spreads 
made  by  drawing  thin  pieces  of  the  organ  over  cover- 
glasses.  These  are  then  fixed  in  the  following: 

Mercuric  chlorid .78  grn. 

Sodium  chlorid       .28  gm. 

Water 30        c.c. 


28  TECHNIC. 

This  solution  should  be  filtered,  and  spreads  fixed  in  it  for 
one  minute.  They  should  then  be  washed  and  stained  one- 
half  hour  with  aqueous  hematoxylin,  washed  and  covered 
with  a  3  per  cent,  solution  of  eosin  for  two  to  three  minutes. 
They  are  then  washed,  dried  and  mounted. 

Spreads  may  be  stained  for  three  minutes  with  eosin,  and 
one-half  minute  with  5  per  cent,  methylene  blue,  then 
washed,  dried  and  mounted. 

Rapid  Technic. — There  is  a  rapid  method  of  technic 
that  gives  good  results.  The  steps  are  as  follows: 

1.  Fix   small    pieces    in   FORMOL-MULLER  SOLUTION   for 
eighteen  to  twenty-four  hours.      (Formol  20  c.c.,  Muller's 
solution  80  c.c.) 

2.  Place  in  95  per  cent,  alcohol  for  two  hours. 

3.  Fresh  95  per  cent,  alcohol  two  hours. 

4.  Absolute  alcohol  (CuSO4),  twelve  to  twenty-four  hours. 

5.  Place  in  anilin  oil  at  52°  C.  until  transparent. 

6.  Place  in  paraffin  at  46°  C.  for  one  hour. 

7.  Place  in  paraffin  at  54°  C.  for  three  to  four  hours. 

8.  Block. 

This  method  requires  about  fifty-six  hours. 

Slide  Technic. — The  preparation  of  sections  for  micro- 
scopic study  requires  skill  and  care. 

Paraffin  sections  are  made  to  adhere  to  the  slide  by  means 
of  MAYER'S  ALBUMEN.  This  is  prepared  by  mixing 
thoroughly  white  of  egg  and  glycerin  in  equal  parts  and 
filtering.  A  very  thin  film  is  all  that  is  necessary. 

The  following  desk  reagents  are  sufficient  for  all  ordinary 
work: 

Coplin  staining  jar,  containing  lodin. 

Coplin  staining  jar,  containing  Kerosene. 

Coplin  staining  jars,  containing  Alcohol.  Nos.  i  and  2. 

One  Barnes  bottle,  containing  Hematoxylin. 


SLIDE    TECHNIC.  2Q 


One  Barnes  bottle,  containing  van  Gieson's 
One  Barnes  bottle,  containing  Eosin. 
One  Barnes  bottle,  containing  Alcohol. 
One  Barnes  bottle,  containing  Water. 
One  Barnes  bottle,  containing  Acid  Alcohol. 
One  Barnes  bottle,  containing  Creosote. 
One  Barnes  bottle,  containing  Albumen. 
One  Barnes  bottle,  containing  Picric  Acid. 

The  method  of  procedure  for  staining  is  given  in  detail 
below  : 

1.  Cover  a  clean  slide  with  a  thin  film  of  albumen. 

2.  Add  a  few  drops  of  water,  and  upon  this  float  the  cut 
paraffin  section. 

3.  Warm  gently  over  a  flame,  so  as  to  spread  the  section, 
but  be  careful  not  to  melt  the  paraffin. 

4.  Drain  and  set  aside,  or  in  an  oven,  for  six  to  twenty- 
four  hours.     The  slide  must  be  perfectly  dry  before  the 
other  step  can  be  carried  out.     Put  on  the  slide  an  identi- 
fication label. 

5.  Place  in  the  kerosene  for  five  to  fifteen  minutes,   to 
remove  the  paraffin.     Xylol  may  be  used. 

6.  Wash  with  alcohol,  to  remove  the  kerosene,  and  place 
in  the  jar  of  iodin,  five  to  ten  minutes,  to  remove  the  crystals 
of  bichlorid  of  the  fixing  agent. 

7.  Remove  the  excess  iodin  from  the  slide  with  tissue 
paper,   wash  with  alcohol  and   place   in    the  first   alcohol 
jar  for  fifteen  minutes,   to  remove  the  remainder  of  the 
iodin. 

8.  Drain  the  section,  wash  with  water,  cover  with  hema- 
toxylin  for  three  to  five  minutes,  and  wash  with  water  to 
deepen  the  color. 

9.  COUNTER-STAIN.  —  Eosin  one   to   two   minutes,    wash 
with  water  to  remove  excess  stain  and  then  alcohol;  or, 


30  TECHNIC. 

Van  Gieson  one-half  to  one  minute,  wash  with  water  and 
then  alcohol,  as  above;  or, 

Picric  acid  fifteen  seconds  and  wash  with  alcohol. 

Carmin  may  be  used  alone  for  fifteen  minutes,  or  followed 
by  picric  acid,  as  in  the  preceding.  If  carmin  is  used  alone 
wash  the  excess  off  with  water  and  then  cover  with  acid 
alcohol  to  differentiate.  When  the  color  becomes  a  brick- 
red,  wash  the  acid  alcohol  off  quickly  with  ordinary  95  per 
cent,  alcohol  and  dehydrate  in  the  usual  way.  Hold  the 
slide  in  the  hand  while  differentiating. 

10.  After  washing  with  alcohol,  dehydrate  in  the  second 
jar  of  alcohol.     Allow  sections  to  remain  about  five  minutes. 

11.  Clean  the  slide  carefully  without  allowing  the  section 
to  dry.     Blot  with  tissue-paper. 

12.  Cover  with  a  drop  or  two  of  creosote  for  Jive  minutes. 
This  removes  the  alcohol,  renders  the  specimen  transparent, 
and  allows  the  use  of  balsam.     This  is  sectional  clearing. 

13.  Drain  off  the  creosote,  blot,  add  a  drop  of  balsam  and 
cover  with  a  clean  cover-glass. 

14.  Remove  the  identification  label,  apply  a  clean  one, 
and  write  the  name  thereon. 

After  the  paraffin  has  been  removed,  the  specimen  should 
never  be  allowed  to  dry. 

The  above  technic  will  answer  for  all  ordinary  histologic 
and  pathologic  work,  and,  if  strictly  adhered  to,  there 
will  not  be  the  slightest  trouble  in  making  excellent 
preparations. 


CHAPTER  II. 


HISTOLOGY. 

Histology  is  the  science  that  treats  of  the  minute  struc- 
ture of  normal  tissues  and  organs.  Although  to  the  naked 
eye  tissues  may  have  an  apparent  structure  that  seems 
ultimate,  when  examined  under  the  microscope  this  struc- 
ture is  seen  to  be  but  gross.  Each  section  studied  will  be 
found  to  be  composed  of  minute  elements,  more  or  less 
regular,  and  definitely  grouped  and  arranged.  These 
elements  are  Cells. 

A  Cell  is  a  small  mass  of  protoplasm  containing  a  nucleus. 
It  is  the  histologic  basis  of  the  body,  and  has  a  complex 
structure.  Certain  parts  are  absolutely  essential  for  the 
proper  performance  of  its  various  functions,  while  others 
are  accessories,  which  most  cells  possess.  The  parts  of  a 
typic  cell  are: 

1.  CELL-BODY. 

2.  NUCLEUS. 

3.  CENTROSOME. 

4.  NUCLEOLUS. 

5.  CELL- WALL. 

i.  The  Cell -body,  or  Protoplasm,  or  Cytoplasm  is  a 
granular,  semi-solid  substance  that  constitutes  the  bulk  of 
the  cell.  It  may  or  may  not  be  limited  by  a  cell -wall. 
It  consists  of  two  main  parts,  the  Spongioplasm,  or  Filar- 
mass,  and  the  Hyaloplasm,  or  Interfilar-mass. 

The  Spongioplasm,  as  its  name  indicates,  is  a  framework 


32  HISTOLOGY. 

of  comparatively  solid  structure,  in  the  meshes  of  which 
is  found  the  semi-fluid  HYALOPLASM.  The  elasticity  of  the 
spongioplasm  is  said  to  give  rise  to  ameboid  movements. 

In  the  protoplasm  are  to  be  seen  small  darkly-staining 
bodies,  the  MICROSOMES,  and  paler  masses,  the  PLASTIDS. 


FIG.  i. — SCHEME  of  a  CELL. — Microsomes  and  spongioplasm  only  partly 
sketched  (Stohr's  Histology). 

i.  Spongioplasm;  2.  hyaloplasm;  3.  microsomes;  4.  exoplasm;  5.  chroma- 
tin;  6.  achromatin;  7. limn;  8.  chromatic  knots;  9.  nuclear  membrane; 
10.  centrosome;  n.  nucleolus;  12  cell-membrane;  13.  inclusions. 


At  the  outer  margin  of  the  cell-body  is  a  narrow,  peripheral 
zone,  containing  no  microsomes,  known  as  the  EXOPLASM. 
At  times  there  are  other  structures  present,  as  fat  globules, 
glycogen,  secretion  granules,  vacuoles,  pigment,  and  crystals. 

The  cell-body  has  affinity  for  acid,  or  protoplasmic, 
stains,  such  as  eosin.  picric  acid,  carmin,  orange,  etc. 

2.  The  Nucleus  is  usually  a  darkly-staining  body  having 


CELL    PROPERTIES.  33 

a  sharp  outline,  and  occupying,  as  a  rule,  a  central  position. 
In  glandular  cell,  its  location  varies  with  the  stage  of 
secretory  activity.  Its  structure  resembles  that  of  the 
protoplasm,  to  a  certain  extent.  It  consists  of  a  network 
and  semi-fluid  substance,  surrounded  by  a  distinct  MEM- 
BRANE or  WALL.  The  network  is  called  the  CHROMATIN,  or 
NUCLEAR  FIBRILS,  and  the  semi-solid  substance,  the 

NUCLEAR  MATRIX,  SAP,  Or  ACHROMATIN. 

CHROMATIN  is  the  part  of  the  nucleus  that  responds  to  the 
stains.  It  is  arranged  as  an  irregular  network  of  anastomos- 
ing fibrils,  each  consisting  of  a  delicate  central  thread,  the 
linin,  upon  which  the  real  chromatin  substance  is  arranged, 
in  the  form  of  granules.  Where  the  chromatin  threads 
cross  each  other  large  masses  of  chromatin  at  times  are 
seen;  these  are  called  karyosomes.  It  is  the  most  im- 
portant portion  of  the  nucleus  during  the  process  of  cell- 
division. 

ACHROMATIN,  or  KARYOLYMPH,  is  the  semi-fluid  substance 
that  fills  the  meshes  of  the  chromatin.  It  reacts  but 
faintly  to  stains,  and  is  not  of  the  same  importance  as  the 
above. 

The  NUCLEAR  MEMBRANE  is  the  wall  that  limits  the  nu- 
cleus. It  is  present  in  nearly  all  nuclei,  stains  readily  and 
is  perforated  for  the  rapid  and  easy  interchange  of  fluids. 
It  consists  of  amphipyrenin. 

Of  the  above  structures,  the  chromatin  persists  through- 
out all  the  stages  of  reproduction,  while  the  remainder  of 
the  nuclear  constituents  disappear. 

3.  The  Centrosome  is  a  small,  darkly-staining  structure, 
which,  owing  to  its  small  size,  has  been  found  in  but  few  of 
the  cells  of  the  human  body.  It  is  readily  seen  and  studied 
in  the  ova  of  some  of  the  lower  animals,  especially  those  of 
ascaris  megalocephala.  It  lies,  usually,  just  outside  of  the 
nucleus,  in  a  small,  clear  field  called  the  ATTRACTION  SPHERE, 

3 


34  HISTOLOGY. 

within  which  are  seen  delicate  lines  that  radiate  from  the 
centrosome.  The  attraction  sphere  and  the  centrosome 
constitute  the  ASTROSPHERE. 

Besides  being  the  center  of  cell-division,  the  CENTROSOME 
seems  to  play  an  important  part  during  the  resting  stage. 
In  pigment  cells  and  white  blood-corpuscles,  it  seems  to 
preside  over  the  movements  of  the  whole  cell,  and  in  ciliated 
and  flagellated  cells  over  the  action  of  these  processes. 

4.  The    Nucleolus   is    a   small    body   found    within    the 
nucleus.     It  is  not  always  present,  and  more  than  one  may 
be  found.     In  nerve  cells  and  ova  it  is  unusually  large  and 
readily  stained,  while  in  others  it  is  scarcely  noticeable. 
Its  importance  is  doubtful,  as  no  definite  function  has  as  yet 
been  found.     It  consists  of  pyrenin,  and  disappears  during 
cell-division. 

5.  The  Cell -wall  is  a  more  or  less  prominent  membrane 
that  limits  cells.     It  is  not  present  in  all  animal  cells,  though 
some  hold  that  even  the  wandering  cells  possess  a  delicate 
membrane.     In  some  instances,  it  consists  of  the  differ- 
entiated, peripheral  protoplasm,  and  in  others,  is  a  secretory 
product  of  the  protoplasm.     When  it  surrounds  the  entire 
cell  it  is  called  a  pellicula;  if  it  is  found  upon  the  exposed 
surface,  as  in  the  intestinal  cells,  it  is  termed  a  cuticular 
border. 

Of  the  above  structures,  the  Cytoplasm,  Nucleus  and 
Centrosome  are  the  essential  parts,  when  the  important 
functions  of  the  cell  are  considered.  In  red  blood-cells  the 
nucleus  is  absent,  and,  as  a  consequence,  these  cells  cannot 
reproduce  themselves. 

Cells  differ  greatly  in  form  and  size;  the  nucleus  conforms 
somewhat  to  the  shape  of  the  cell.  Usually  but  one  is 
present,  but  in  giant  cells  and  voluntary  striated  muscle, 
many  are  to  be  found. 

The  cell,  like  the  organism,  exhibits  a  number  of  proper- 


CELL    PROPERTIES.  35 

ties,  such  as  Metabolism,  Growth,  Motion,  Irritability  and 
Reproduction. 

Metabolism  is  the  change  that  takes  place  in  a  cell  during 
the  performance  of  its  functions.  When  the  result  is  the 
formation  of  complex  structures,  the  process  is  called 
ANABOLISM;  if  destructive,  the  conversion  of  complex  to 
simple  compounds,  the  phenomenon  is  termed  KATABOLISM. 
SECRETION  and  EXCRETION  are  anabolic  changes,  as  simple 

Chromosomes.  Centrosome. 


FIG.  2. — SCHEME  OF  THE  CLOSE  COIL  AND  THE  DIVISION  OF  THE  CENTRO- 
SOMES  (Stohr's  Histology). 

structures  are  converted  into  complex  compounds.  Secre- 
tion may  be  glandular  secretion,  or  simply  an  intercellular 
substance  may  be  formed. 

Growth  is  the  result  of  an  anabolic  process.  The  cells 
increase  in  size,  equally  or  more  often  unequally,  depending 
upon  the  organ.  When  the  latter  occurs,  the  cell-form  is 
changed.  By  such  a  change  in  all  cells,  the  organism  in- 
creases in  size,  though  the  amount  contributed  by  each  cell 
may  be  microscopic. 

Motion. — But  few  cells  possess  this  property  to  any  great 
extent.  The  ameboid  leukocytes  show  it  best  as  they  may 
pass  from  one  part  of  the  body  to  another.  One  of  the  most 


36  HISTOLOGY. 

characteristic  examples  of  this  property  is  exhibited  by  the 
muscles,  especially  the  voluntary  striated  variety;  here, 
although  the  whole  cell  moves,  the  motion  is  limited  to  one 
direction.  Motion  may  be  limited  to  only  a  portion  of 
the  cell,  as  to  hair-like  processes  called  cilia. 

Irritability  is  the  property  of  response  to  surrounding  in- 
fluences or  stimuli.  This  is  more  pronounced  in  the  in- 
dividual cells  of  such  animals  that  possess  no  nerve 
system.  Here  it  is  practically  a  primary  change  in  the  cell. 

Central  spindle. 


\ 


FIG.  3. — SCHEME  OF  THE  LOOSE  COIL  AND  SEPARATION  OF  THE  CENTROS<  >MI:S 
(Stohr's  Histology). 

When  a  nerve  system  is  present,  this  presides  over  such 
changes  which  are  then  secondary. 

Reproduction  is  the  process  by  means  of  which  a  cell  or 
an  organism  propagates  itself  and  continues  its  life  history. 
Without  this  or  an  analogous  process,  life  would  soon  cease 
to  exist.  It  is  of  two  varieties,  DIRECT,  AMITOSIS  or  BUDDING 
and  INDIRECT,  MITOSIS  or  KARYOKINESIS.  Of  these,  the 
latter  is  the  more  common. 

In  Amitosis,  the  cell-body  is  marked  by  a  constriction 
that  gradually  deepens  and  is  imparted  to  the  nucleus. 


CELL-DIVISION.  37 

As  tnis  deepens,  the  protoplasm  and  nucleus  are-  finally 
divided  into  two  small  but  practically  equal  cells,  which 
have  the  same  structure  as  the  parent  cell.  By  growth, 
these  cells,  which  are  called  daughter  cells,  increase  in  size, 
until  that  of  the  parent,  or  mother,  cell  is  attained. 

This  form  of  division  is  seen  in  the  bladder  epithelium 
in  mammals  and  in  the  cells  of  Sertoli  of  the  testicle. 

Mitosis  is  a  very  complex  process,  in  which  the  nucleus 
plays  a  very  important  part.  The  protoplasm  is  almost 

Polar  radiation.  Central  spindle. 


FIG.  4. — SCHEME  OF  THE  MOTHER  STAR,  OR  EQUATORIAL  PLATE  (Stohr's 

Histology). 

passive  until  the  late  stages  of  the  process.  The  various 
stages  are  the  PROPHASE,  METAPHASE,  ANAPHASE  and 
TELOPHASE.  These  are  not  absolutely  separable  from  one 
another.  The  changes  that  occur  may  be  grouped  under 
three  heads — nuclear,  centrosomic  and  protoplasmic. 

PROPHASE. — The  nuclear  changes  are  quite  complex. 
Whereas  the  chromatin  is  ordinarily  arranged  as  an  ir- 
regular network,  when  division  begins  the  irregular  twigs 
of  the  network  gradually  become  smooth,  and  form, 
usually,  a  single  thin  closely-convoluted  thread,  called  the 
SPIREM,  or  SKEIN.  The  thread  becomes  thicker  and  shorter, 


30  HISTOLOGY. 

and  soon  separates  into  a  number  of  segments  called 
CHROMOSOMES.  This  sometimes  occurs  before  the  spirem 
is  formed.  The  chromosomes  become  U-  or  V-shaped,  and 
arrange  themselves  along  the  equator  of  the  cell  writh  the 
closed  ends  directed  toward  a  common  center,  called  the 
polar  field.  This  arrangement  is  termed  the  EQUATORIAL 
PLATE,  or  MONASTER,  and  practically  ends  the  chromatin 
changes  during  the  PROPHASE. 


FIG.    5. — SCHEME   OF   METAKINESIS,    SHOWING    THE    NUCLEAR    SFINDI  i: 
(Stohr's  Histology'). 

The  CHROMOSOMES  are  always  even  in  number,  and  the 
same  number  is  always  formed  in  each  cell  of  the  same 
species.  In  man,  the  number  is  said  to  be  sixteen  or 
twenty-four. 

The  nuclear  membrane,  during  these  changes,  has  gradu- 
ally become  more  and  more  hazy,  and  finally  disappears. 
The  achromatin  is  released,  and  mixes  with  the  protoplasm. 

The  nucleolus  likewise  gradually  fades  and  disappears. 

The  centrosome  is  the  dynamic  center  of  *  the  cell.  It  di- 
vides into  two  portions  (if  within  the  nucleus,  it  passes  first 
into  the  protoplasm),  each  of  which  becomes  surrounded  by 
its  own  attraction  sphere.  These  centrosomes  gradually  move 
apart,  through  an  arc  of  90°,  to  opposite  poles  of  the  cell. 
During  this  change,  some  of  the  intervening  rays  remain  in 


KARYOKINESIS. 


39 


contact,  forming  a  spindle  of  delicate  threads,  which  is  com- 
plete when  the  centrosomes  reach  their  polar  position. 
This  is  the  CENTRAL,  or  ACHROMATIC  SPINDLE,  and  the 
threads  are  of  the  utmost  importance,  and  become  attached 
to  the  chromosomes  of  the  equatorial  plate. 

With  the  formation  of  the  equatorial  plate  and  central 
spindle,  the  PROPHASE  ends.  Variations,  too  numerous  to 
describe,  occur,  but  the  above  is  the  usual  course  in  this 
stage  of  mitosis. 


FIG.  6.— SCHEME  OF  THE  DAUGHTER      FIG.  7.— SCHEME  OF  DIVISION  OF 
STARS  THE  PROTOPLASM  FORMING 

DAUGHTER  CELLS. 
(Stohr's  Histology}. 

METAPHASE.— This  is  the  stage  during  which  the  chromo- 
somes divide  and  separate.  It  concerns  the  chromatin 
chiefly. 

The  chromosome  divide  longitudinally  into  two  equal 
portions.  This  cleavage  occurs  at  the  closed  end  first,  and 
as  it  proceeds,  the  daughter  chromosomes  become  separated, 
one-half  being  drawn  toward  the  one  centrosome,  and  the 
other  toward  the  second.  This  gives  rise  to  a  second 
spindle,  the  NUCLEAR,  or  CHROMATIC  SPINDLE.  The 
separation  is  affected  by  the  traction  exerted  upon  the 
daughter  chromosomes  by  the  threads  of  the  central  spindle. 

ANAPHASE. — This  is  the  stage  of  complete  separation  of 


40  HISTOLOGY. 

the  chromosomes.  The  latter  collect  around  their  respect- 
ive centrosome,  and  remain  connected  to  the  opposite  set, 
for  some  time,  by  the  central  spindle  threads.  The 
figures  thus  formed  are  the  DIASTERS,  or  DAUGHTER  STARS. 

TELOPHASE. — This  stage  is  concerned  with  the  protoplas- 
mic changes  and  the  formation  of  a  resting  nucleus.  Up  to 
this  time,  the  protoplasm  has  been  practically  quiescent. 

The  chromosomes  collect  around  the  centrosomes,  and 
unite  to  form  a  close  skein.  Lateral  twigs  are  developed 
that  anastomose  to  form  the  nuclear  network,  a  nuclear 
membrane  is  formed  and  a  nucleolus  appears. 

The  hitherto  inert  protoplasm  shows  changes.  A  double 
row  of  vacuoles  appears  at  the  equator  of  the  cell,  and 
separation  occurs  in  the  intervening  space  until  two  sepa- 
rate masses  are  formed;  these  are  the  DAUGHTER  CELLS. 

The  above  changes  are  usually  succeeded  by  a  period  of 
rest. 

Although  apparently  a  long  process,  only  about  one-half 
hour  is  consumed  in  the  division  of  human  cells,  but  the  cells 
of  lower  animals  require  a  longer  period. 

In  the  case  of  giant  cells,  the  nucleus  divides  and  redivides, 
while  the  protoplasm  remains  unchanged.  They  may  also 
be  formed  by  the  fusion  of  the  protoplasm  of  a  number  of 
cells  with  the  retention  of  the  individuality  of  the  nuclei. 

As  all  cells  are  developed  from  preexisting  elements,  it 
is  but  natural  that  the  original  cell  of  the  body,  the  Ovum, 
should  be  of  greatest  interest.  It  is  the  most  characteristic 
cell  of  the  body,  and  is  secreted  by  the  ovary.  It  is  the 
largest  cell,  and  illustrates  the  individual  parts  well. 

The  Ovum  consists  of  a  limiting  wall,  the  vitelline  mem- 
brane, that  is  well  developed.  Within  this  is  the  proto- 
plasm, vitellus,  which  consists  of  two  parts — the  DEUTO- 

PLASM,    or  NUTRITIVE   YOLK,    and    the  ANIMAL   PROTOPLASM, 

or  FORMATIVE  YOLK.     This  is  of  importance,  embryologically. 


MATURATION.  41 

Within  the  vitellus  is  found  the  nucleus,  or  germinal 
vesicle,  which  contains  a  deeply  stained  nucleolus,  or 
germinal  spot.  The  centrosome  is  to  be  seen  in  unripened 
ova.  After  maturation  this  body  disappears.  In  what 
might  be  termed  an  embryologic  ovum,  there  are  two  layers 
external  to  the  vitelline  membrane,  the  ZONA  PELLUCIDA 
and  the  CORONA  RADIATA.  Of  these,  the  former  is  the  more 
important,  because  of  the  part  which  it  plays  in  the  early 
stages  of  development. 


FIG.  8. — UNRIPENED  OVUM  FROM  A  YOUNG  GUINEA-PIG. 
A,  Nucleus;  B,  nucleolus;  C,  centrosomes  in  the  attraction  sphere. 

There  are  a  number  of  processes  that  occur  in  the  ovum 
before  it  can  develop  into  an  offspring.  Of  these,  the  most 
important  are  MATURATION  and  FERTILIZATION.  The 
former  occurs,  usually,  in  the  ovary,  and  the  latter,  as 
a  rule,  in  the  Fallopian  tube. 

Maturation  is  the  process  by  which  part  of  the  chromatin 
and  a  small  portion  of  the  protoplasm  are  extruded  in  the 
form  of  two  minute  structures  called  POLAR  BODIES.  It 
is  a  modified  karyokinesis,  and  its  object  is  unknown.  All 
ova  must  pass  through  this  process  before  they  can  be 
fertilized. 


42  HISTOLOGY. 

Fertilization  is  the  process  in  which  the  male  and  female 
elements  unite  to  form  a  complete  and  perfect  cell,  which, 
by  division,  gives  rise  to  the  cells  that  ultimately  form 
the  whole  body. 

The  male  element,  or  spermatozoon,  or  spermium,  consists 
of  HEAD,  MIDDLE-PIECE  and  TAIL.  Of  these  the  HEAD  and 
MIDDLE-PIECE,  representing  the  NUCLEUS  and  CENTROSOME, 
respectively,  of  a  cell  of  the  testicle,  enter  the  ovum  and 
form  eight  *  chromosomes.  The  chromatin  of  the  germinal 
vesicle  of  the  ovum  also  forms  eight.  By  longitudinal 
cleavage  thirty-two  are  formed  of  which  sixteen  enter  into 
each  diaster  and,  consequently,  each  daughter  cell.  By 
this  process  the  descendants  of  the  fertilized  ovum  contain 
double  the  number  of  chromosomes  that  existed  in  either  of 
the  original  cells  before  fertilization. 

After  fertilization  the  ovum  divides  and  redivides,  forming 
an  irregular  mass  of  cells  called  the  Morula,  or  Mulberry 
Mass.  Certain  of  these  cells  form  a  complete  layer  that 
surrounds  the  remainder,  which  constitutes  an  irregular 
mass.  The  layer  is  the  OUTER  CELL-MASS  and  the  latter 
the  INNER  CELL-MASS.  This  structure  constitutes  the 
Blastula,  or  one-layered  vesicle.  Of  these  two  structures 
the  inner  is  the  more  important  as  it  persists  and  forms 
the  whole  body  while  the  outer  is  said  to  disappear. 

The  INNER  CELL-MASS  forms  two  layers,  an  outer,  several 
cells  in  thickness,  the  ECTODERM,  or  EPIBLAST,  and  an 
inner,  composed  of  but  a  single  layer,  the  ENTODERM,  or 
HYPOBLAST.  This  is  the  Gastrula,  or  Diploblast.  The 
ectoderm  and  entoderm  each  set  aside  a  number  of  cells 
which  by  multiplication  form  a  third  layer,  the  MESODERM, 
or  MESOBLAST,  that  lies  between  the  two.  This  structure 
receives  the  name  of  Blastodermic  Vesicle,  or  Triploblast. 

*  Some  writers  claim  the  somatic  cell  contains  sixteen  chromosomes 
while  others  say  there  are  twenty-four. 


DERIVATIVES    OF    THE    TRIPLOBLAST.  43 

From  these  three  primitive  layers  all  the  orgens  and 
tissues  of  the  body  are  formed  as  follows: 

ECTODERM. 

The  nerve  system  (cerebrospinal  and  sympathetic)  the 
retina,  the  bulk  of  the  crystalline  lens,  the  muscle  of  the 
iris  and  part  of  the  vitreous  humor  of  the  eyeball,  the  epi- 
thelium of  the  cornea  and  conjunctiva,  the  epithelium  of 
the  internal  ear  and  of  the  olfactory  organ,  the  medulla  of 
the  adrenal. 

The  epithelial  lining  of  the  anterior  portion  of  the  male 
urethra,  the  labia  of  the  female  and  the  glands  leading 
thereto. 

The  epithelial  lining  of  the  mouth  and  salivary  glands, 
epithelial  lobe  of  the  pituitary  body,  the  enamel  of  the 
teeth,  the  cells  of  the  nasal  tract  and  glands  leading  thereto, 
to  the  pharynx,  and  the  lining  of  the  anus. 

The  epidermis  and  appendages  of  the  skin,  muscles  of 
the  sweat  glands. 

The  syncytium  of  the  placenta. 

ENTODERM. 

The  epithelial  lining  of  the  bladder,  the  prostate  and 
glands  of  Cowper,  of  the  first  and  second  portions  of  the 
male  and  entire  female  urethra,  vestibule  and  glands  of 
Bartholin. 

The  epithelium  of  the  tongue,  thymus  and  thyroid  bodies 
of  the  parathyroids,  middle  ear  and  Eustachian  tube. 

The  epithelium  of  the  alimentary  and  respiratory  tracts 
from  the  mouth  and  posterior  nares  down  and  the  epithelium 
of  all  glands  opening  into  these  structures. 

The  notochord. 

MESODERM. 

The   vascular  system. 

The  lymphatic  system  including  the  large  serous  cavities, 
spleen  and  thymus  body  (except  the  corpuscles  of  Hassal). 


44  HISTOLOGY. 

The  muscle  tissues  (except  the  muscles  of  the  sweat- 
glands  and  iris). 

The  connective  tissues. 

Testicle,  vas,  seminal  vesicles,  ejaculatory  duct,  ovary, 
oviducts,  uterus  and  vagina. 

Kidneys,  ureters  and  cortex  of  adrenal. 


CHAPTER  III. 


THE  TISSUES. 

From  the  preceding  table  it  will  be  seen  that  all  tissues 
are  developed  from  the  three  layers  of  the  triploblast. 
These  tissues  are  grouped,  histologically,  under  four  classes, 
Epithelial,  Connective,  Muscle  and  Nerve. 

A  Tissue  consists  of  similarly  differentiated  cells  held  to- 
gether by  intercellular  cement,  and  performing  a  definite 
function.  The  intercellular  substance  varies  with  the 
different  tissues.  The  cells  of  a  tissue  may  be  so  arranged 
as  to  form  an  organ  or  merely  a  supporting  structure. 

Epithelium. 

The  Epithelial  Tissues  are  characterized  by  the  small 
amount  of  the  intercellular  cement.  The  cellular  elements 
are  usually  prominent,  and  rich  in  granular  protoplasm. 
They  are  found  lining  cavities  that  communicate  normally 
with  the  air  and  usually  secrete,  although  they  may  also 
have  an  excretory,  absorptive,  or  protective  function. 
They  are  avascular  and  may  be  derived  from  any  of  the 
layers  of  the  triploblast.  The  cells  very  in  size,  form  and 
arrangement,  as  will  be  seen  later. 

For  convenience  of  description,  the  cells  are  classified  as 
follows : 

1.  Squamous.  3.  Ciliated. 

a.  SIMPLE.  e.  SIMPLE. 

b.  STRATIFIED.  f.  STRATIFIED. 

2.  Columnar.  4.  Prickle  cells. 

c.  SIMPLE.  5.  Goblet  cells. 

d.  STRATIFIED.  6.  Transitional  cells. 
Modified. 


46 


THE    TISSUES. 


7.  Pigmented. 
Specialized. 


8.  Neuro -epithelial. 

9.  Glandular. 


i.  Squamous.    a.    The    SIMPLE    SQUAMOUS    cells    consist 
of  a  single  layer  of  flattened  elements,  each  containing  a 


FIG.  9. 
a.  Simple  squamous  cells,     b.  Simple  cuboidal  cells. 

large  nucleus.  This  is  usually  in  the  center,  and  has  an 
oval,  or  round  form.  They  occur  in  the  descending  limb  of 
Henle's  loop,  the  capsule  of  Bowman  in  the  kidney,  the 


FIG.  ii. — SQUAMOUS  CELL  ISOLATKD. 


FIG.  10. — SURFACE  VIEW  OF  SQUAM-        FIG.    12. — STRATIFIED   SQUAMOUS 
ous  CELLS  OF  FROG'S  SKIN.  EPITHELIUM. 

alveoli  of  the  lungs,  and  in  parts  of  the  ventricles  of  the 
brain. 

b.  The  STRATIFIED  SQUAMOUS  variety  consists  of  many 
layers  of  cells  that  are  unlike  in  form.     The  lowest  layer, 


EPITHELIAL    CELLS. 


47 


the  germinal  stratum,  is  columnar,  while  those  ceils  just 
above  are  polygonal.  The  succeeding  cells  become  more 
and  more  flattened,  forming  the  squames,  or  scales,  from 
which  this  variety  receives  its  name.  It  is  found  covering 
the  body  as  the  epidermis,  lining  the  mouth,  pharynx, 


FIG.  13. 

a.  Simple  Columnar  showing  Cuticular  Border,     b.  Simple  Ciliated  Cells. 
c.  Simple  Columnar  and  Goblet  Cells. 

esophagus,  epiglottis,  vocal  cords  and  the  anus  and  vagina. 
2.  Columnar,  c.  SIMPLE  COLUMNAR  cells  are  tall,  cylindric 
elements  arranged  in  a  single  layer.  The  nucleus  is  usually 
oval,  and  found  nearer  the  base  than  the  center  of  the  cell. 
The  variety  is  found  in  the  stomach  and  intestinal  tract, 


FIG.  14. 

0.  Isolated  Columnar  Cells,     b.  Isolated  Ciliated  Cells,     c.  Three  Stages 
of   Goblet   Cells. 

the  penile  portion  of  the  urethra,  glands  of  Cowper,  and 
Bartholin,  prostate,  gall-bladder  and  seminal  vesicles, 
and  in  many  gland  ducts.  In  the  intestine  these  cells, 
upon  their  exposed  surface,  have  a  layer  of  differentiated 
protoplasm  forming  a  partial  membrane;  this  is  called  a 
cniicular  border.  Low  columnars  are  often  called  cuboidal. 


48  THE    TISSUES. 

PSEUDOSTRATIFIED  cells  are  simple  columnar,  or  ciliated, 
cells,  in  which  the  nuclei  are  not  all  basal,  but  occupy  differ- 
ent levels,  thus  giving  the  appearance  of  several  layers  of 
cells,  where,  in  reality,  but  a  single  layer  exists.  These  are 
found  as  ciliated  elements  in  the  oviducts,  uterus  and 
middle  ear  and  as  non-ciliated  elements  in  the  seminal 
vesicles  (maybe  simple)  and  prostate,  according  to  some 
writers. 

d.  STRATIFIED  COLUMNAR  cells  consist  of  a  number  of 
layers  of  columnar  elements  superimposed  upon  one 


FIG.  15. — PSEUDOSTRATIFIED  CELLS. 

another.  The  cells  are  not  as  large  as  the  preceding. 
They  occur  in  the  vas  deferens,  membranous  urethra  and 
the  ducts  of  some  glands. 

3.  Ciliated    cells,    e.  SIMPLE  CILIATED    cells  are  simple 
columnar  elements,  which  bear,  upon  their  exposed  surface, 
a  varying  number  of  hair-like  processes  called  cilia.     These 
possess  a  motion  that  is  directed  toward  the  outlet  of  the 
organ    in    which    these    cells    are    found.     They   line    the 
smaller  bronchioles,  spinal  canal,  accessory  spaces  of  the 
nasal  fossae  and  the  ventricles  of  the  brain. 

f .  The  STRATIFIED  CILIATED  cells  are  practically  stratified 
columnar  cells,  of  which  the  exposed  layer  alone  possesses 
cilia.  They  are  found  in  the  epididymis,  first  part  of  the 
vas,  Eustachian  tube,  upper  part  of  the  pharynx,  in  the 
larynx,  trachea  and  nasal  tract. 

4.  Prickle  cells  are  polygonal  elements  that  possess  little 
spines,  which  project  from  the  sides  of  the  cells.     These, 


EPITHELIAL    CELLS. 


49 


meeting  the  spines  of  other  cells,  prevent  the  ce41-bodies 
from  touching.  In  this  way,  a  series  of  intercellular 
bridges  and  spaces  is  formed.  These  cells  are  found  in  the 
epidermis,  just  above  the  genetic  layer. 


FIG.  16. 

a.  Stratified    Columnar    Cells,     b.  Stratified    Ciliated    Cells. 
Columnar  Cells  showing  Goblet  Cells. 


c.  Stratified 


5.  Goblet  cells  are  cells  of  the  cylindric  type,  distended 
with  a  peculiar  secretion  called  mucin.  When  filled,  they 
resemble  a  goblet,  hence  the  name.  When  the  secretion  has 
been  discharged,  the  cells  are  long  and  slender,  the  part  con- 
taining the  nucleus  projecting  on  either  side.  Such  cells 
are  met  with  in  the  gastro-intestinal  and  respiratory  tracts. 


FIG.  17. — TRANSITIONAL  CELLS. 

6.  Transitional  cells  are  peculiar  stratified  elements  that 

are   neither   columnar   nor   squamous.     They   occupy   an 

intermediate  position,  as  all  the  cells  are  polygonal.     They 

occur  in  the  pelvis  of  the  ureter,  in  the  ureter,  bladder,  the 

4 


50  THE    TISSUES. 

first  portion  of  the  male  and  the  greater  portion  of  the 
female  urethra. 

7.  Pigmented  cells  are  polygonal  or  columnar  cells,  in 
which  the  protoplasm  contains  a  varying  number  of  pig- 
ment granules.     The  former  shape  is  found  in  the  epidermis 
of  colored  races,   and  around   the  nipple  and  genitals  of 
Caucasians;  the  latter  occurs  in  the  retina  of  the  eye,  and 
the  pigment  granules  obscure  the  various  parts  of  the  cell. 

8.  Neuro -epithelial   cells   are   epithelial   cells   that  have 
become   so   differentiated   as    to   perform   a   special   sense 
function.     They  differ  according  to  location,  and  will  be 
described   under  each  special  sense.     They  occur  in   the 
retina   (rods  and  cones),   in   the    internal    ear   (hair  cells), 
in  the  olfactory  mucous  membrane,  in  the  taste-buds  and 
as  tactile  cells. 

9.  Glandular  cells  also  vary  according  to  the  nature  of 
the  gland  in  which  they  are  found,  as  in  the  liver,  pancreas, 
etc. 

Mucous  Membranes. — The  epithelial  surfaces  within  the 
body  are  termed  Mucous  membranes.  Glands,  which  are 
evaginations  of  such  surfaces,  are  also  classed  with  mucous 
membranes.  Such  membranes  are  complexes  of  all  four 
varieties  of  tissues.  They  are  lined  by  EPITHELIAL  CELLS, 
of  any  of  the  varieties  above  mentioned,  that  rest  upon  a 
delicate  BASEMENT  MEMBRANE,  beneath  which  is  found  a 
layer  of  fibro-elastic  tissue  called  the  TUNICA  PROPRIA. 
Here  are  seen  nerves,  capillary  blood-vessels,  lymphatic 
channels  or  spaces,  and,  in  certain  organs,  glands  and  lymph- 
oid  tissue.  The  structure  is  limited,  peripherally,  by  a 
layer  of  involuntary,  nonstriated  muscle  tissue,  the  MUS- 
CULARIS  MUCOS^.  The  latter  is  not  always  present,  as 
will  be  seen  when  the  various  organs  are  studied  in  detail. 
These  membranes  line  cavities  that  communicate  normally 
with  the  air  and  usually  secrete. 


MUCOUS   AND    SEROUS    MEMBRANES.  51 

As  some  writers  classify  Endothelial  cells  as  epithelial,  it 
is  well  to  consider  them  at  this  time,  so  as  to  contrast  them. 

Endothelial,  or,  better,  Mesothelial,  cells  are  thin,  flat- 
tened elements  possessing  a  large  projecting  nucleus.  They 
are  irregular  in  outline,  and  are  held  together  by  inter- 


FIG.  18. 

A. — ABDOMINAL  EXDOTHELIUM.  a.  Endothelial  cell;  b.  nucleus  of  cell; 
c.  cell  boundary;  d.  stigmata;  e.  endothelial  cells  of  stomata;  /.  sto- 
mata.  B. — MESENTERIC  ENDOTHELIUM.  C. — ARTERIAL  ENDOTH- 
ELIUM.  D. — PERIVASCULAR  LYMPHATICS,  a.  Endothelial  cells  of 
lymphatics;  b.  blood-vessel  (arteriole). 

cellular  cement.  They  never  occur  in  more  than  a  single 
layer,  and  form,  with  fibro-elastic  supportive  tissue,  the 
subendothelial  connective  tissue,  a  Serous  Membrane.  A 
Serous  Membrane  possesses  neither  basement  membrane  nor 
muscularis  miicosa,  and  lines  cavities  that  do  not  com- 
municate normally  with  the  air  and  never  secretes.  Such 


52 


THE    TISSUES. 


membranes  are  smooth,  moist,  glistening  and  transparent, 
and  subject  to  inflammations  different  from  those  of  the 
foregoing.  Openings  called  stomata  are  said  to  exist,  but 
these  are  now  considered  artifacts. 

Serous  membranes  are  found  lining  joint-cavities, 
bursae,  tendon  sheaths,  the  circulatory  and  lymphatic 
systems  and  the  larger  serous  cavities,  the  pleural,  periton- 
eal and  pericardial. 


CHARACTERISTICS. 


MUCOUS    MEMBRANES. 


SEROUS    MEMBRANES. 


Where  found 


Lined  by 


Secrete  . 
Structure  . 


Represents    . 


Lining  cavities  that 
communicate  nor- 
mally with  the  air. 


Epithelial  cells  of  any 
variety. 

With  few  exceptions- 
Epithelial  cells,  base, 
ment  membrane,  tu- 
nica propria,  muscu- 
laris  mucosae. 
All    four    varieties    of 
tissue. 


In  cavities  that  do  not 
normally  communi- 
cate with  the  air  (fe- 
male peritoneal  cav- 
ity excepted). 

Endothelial  (Meso- 
thelial)  cells,  one 
layer. 

Do  not. 

Endothelial  cells,  sub- 
endothelial  connec- 
tive tissue. 

But  two  varieties  (nei- 
ther muscle  nor  epi- 
thelial tissues). 


GLANDS. 

A  description  of  epithelial  tissues  would  not  be  complete 
without    a    consideration    of    Glands.     Glands    may    be 

UNICELLULAR,   as    the  GOBLET-CELL,    Or  MULTICELLULAR,   as 

those  that  will  be  considered  below.  A  Gland  is  an  evagina- 
tion  of  a  mucous  surface,  consists  of  epithelial  cells,  ar- 
ranged in  definite  groups,  and  performs  a  physiologic 


GLANDS.  53 

function.  These  groups  are  the  secretory  units  of  the 
organ. 

Glands  may  be  classified  in  several  ways:  i,  as  to 
Structure,  2,  as  to  Secretion,  and  3,  as  to  Outlet. 

i.  Structure. — As  the  secretory  units  are  of  different 
shapes  we  have  the  following  divisions  and  subdivisions : 

Tubular  Glands. 

SIMPLE. 

BRANCHED. 

COILED. 

COMPOUND. 

Tubulo -alveolar  Glands. 
Alveolar,  or  Racemose  Glands. 

SIMPLE. 

COMPOUND. 

Tubular. — SIMPLE  TUBULAR  glands  are  mere  cylindric 
depressions  in  the  mucous  membrane.  They  are  lined, 
usually,  by  simple  columnar  cells.  They  occur  in  the 
cardiac  end  of  the  stomach,  and  in  the  small  and  large 
intestines. 

The  branched  tubular  are  like  the  above,  except  that  the 
lower  end  is  divided  into  two  or  more  secretory  units. 
The  lining  cells  may  be  columnar,  or  ciliated,  as  in  the 
uterus.  These  glands  are  found  in  the  fundus  and  pyloric 
portion  of  the  stomach,  in  the  duodenum  (Brunner's 
glands),  in  the  uterus,  and  in  the  prostrate. 

Coiled  tubular  glands  are  really  simple  tubes,  the  secre- 
tory portion  of  which  has  become  coiled  and  convoluted  to 
occupy  as  small  a  space  as  possible.  The  lining  cells  are 
columnar  or  cuboidal  (low  columnar).  Examples  are  the 
sweat  and  ceruminous  glands. 

Compound  tubular  glands  are  those  in  which  the  prim- 
tive  tubules  have  divided  and  redivided  until  an  enormous 


54 


THE    TISSUES. 


number  of  divisions  has  resulted.     Pure  examples  of  this 
variety  are  the  liver   (also  called  reticular),   testicle,  kid- 


FIG.    19. — GLAND   OF   LIEBERKUEHN   FROM   A   SECTION   OF   THE    LARGE 

INTESTINE. 
a.  Lumen;  b.  secretion  of  cells;  c,  nucleus  and  protoplasm  of  cell;  dfundus 

cells  at  the  beginning  of  secretion;  e.  f.  goblet  cells  in  later  stage;    g. 

dying  goblet  cells  (Stohr's  Histology'). 

ney,    thyroid,   lacrimal    and   serous  glands  of  the  mucous 
membranes. 


GLANDS. 


55 


Tubulo -alveolar  glands  are  those  in  which  the  terminal 
tubules  possess  sac-like  evaginations  along  the  walls. 
Such  glands  are  the  sub  maxillary,  sublingual,  mammary 
and  the  lungs. 


FIG.  20. — DIAGRAMS  OF  TUBULAR 

GLANDS  (Stohr's  Histology}. 
A.    Simple    tubular;    B.  branched 
tubular;  a.  excretory  duct;  C. 
compound  tubular. 


FIG.    21. — ALVEOLO-TUBULAR 
GLANDS  (Stohr's  Histology}. 
Branched     alveolo-tubular;      2. 

compound  alveolo-tubular ;    a. 

excretory  duct. 


Alveolar. — The  SIMPLE  ALVEOLAR,  or  saccular,  glands  are 
sac-like  depressions  extending  from  the  free  surface.  They 
are  comparatively  few  in  number,  and  occur  as  the  smallest 
sebaceous  glands. 

The  COMPOUND  RACEMOSE  glands  are  like  the  compound 
tubular,  except  that  the  terminal  portions  are  saccular, 


56  THE   TISSUES. 

instead  of  tubular.     Such  glands  are  the  pancreas,  parotid, 
and  the  large  sebaceous  glands. 

2.  Secretion. — The  function  of  a  gland  is  to  give  rise  to  a 
substance  to  be  used  by  the  body  in  some  of  its  many 
processes.  This  substance  is  called  a  secretion,  and  it  may 
be  liquid  or  cellular  (ovum).  The  liquid  secretions  may 


Fig.  22. — Alveolar  Glands  (Stoh^s  Histology). 
i.  Alveolar  system;  2.  compound  alveolar  gland;  a.  excretory  duct. 

be  serous,  mucous,  or  mixed.  These  terms,  applied  to  the 
respective  glands  as  well,  have  reference  to  the  salivary 
glands  alone. 

SEROUS  glands  are  those  which  form  a  thin  albuminous 
secretion.  The  glandular  cells  respond  well  to  stains. 
The  parotid  and  pancreas  belong  to  this  class. 

Mucous  glands  are  those  that  give  rise  to  a  thick  viscid 
substance.  The  cells  here  stain  but  lightly  with  the 


GLANDS.  57 

ordinary  stains.  Such  are  the  small  glands  found  in  the 
mouth,  esophagus,  trachea  and  the  sublingual,  according 
to  some  writers. 

MIXED  glands  are  those  in  which  both  varieties  of  secre- 
tion are  formed.  The  secretory  areas  are  stained  darkly 
or  lightly,  according  to  whether  they  are  serous  or  mucous. 
The  sublingual  and  submaxillary  glands  are  examples,  and 
of  these,  the  latter  is  the  more  characteristic. 

The  minute  structure  of  these  glands  will  be  considered 
under  the  Alimentary  Tract. 

The  excretory  glands  are  the  kidneys,  lungs  and  sweat 
glands.  Each  will  be  considered  in  detail,  under  its  re- 
spective system. 

3.  Outlet. — As  a  rule,  all  glands,  at  some  period  in  their 
development,  are  connected  with  the  mucous  surface  by  a 
tube  called  a  duct.  This  connection,  in  most  instances, 
persist,  but  where  it  disappears,  the  gland  becomes  isolated, 
and  the  term  ductless  gland  is  applied.  Such  are  the  ad- 
renals, hypophysis  and  thyroid  bodies,  parathyroid,  carotid 
and  coccygeal  glands,  the  ovary  and  the  areas  of  Langer- 
hans  in  the  pancreas.  These  form  an  internal  secretion 
that  is  absorbed  by  the  circulatory  or  lymphatic  system. 
Those  with  ducts  pour  their  secretions  or  excretions  into 
the  various  tracts  with  which  they  are  connected. 


CHAPTER  IV. 

CONNECTIVE  TISSUES. 


The  Connective  Tissues  are  the  supportive  tissues  of 
the  body.  They  are  characterized  by  the  predominance  of 
the  intercellular  substance  over  the  cellular  elements.  This 
intercellular  substance  varies  in  the  different  forms,  as  will 
be  seen  when  each  is  considered.  Connective  tissues 
are  usually  vascular  and  are  derived  entirely  from  the 
mesoderm. 

For  the  convenience  of  description,  this  class  has  been 
subdivided  into  the  following  varieties: 

Fibrous.  Modified. 

1.  WHITE.  6.  ADIPOSE. 

a.  Loose.  7.  LYMPHOID. 

b.  Dense.  8.  CARTILAGE. 

2.  YELLOW  ELASTIC.  9.   BONE. 

3.  Mucous.  10.  DENTIN. 

4.  RETIFORM.  n.   BLOOD. 

5.  MIXED. 

The  Fibrous  varieties  are  characterized  by  the  fibrous  or 
semi-solid  intercellular  substance.  The  cellular  elements 
are  comparatively  few,  and  are  found  scattered  among  the 
fibrils.  There  are  several  varieties  of  cells  found  in  con- 
nective tissues.  These  are  the  TRUE,  or  FIXED,  the  WANDER- 
ING and  the  PLASMA  cells.  The  TRUE,  or  FIXED,  connective 
tissue  cell  is  a  flattened,  stellate  element  with  many  proc- 
esses that  extend  in  all  directions,  and  anastomose  with 
those  of  other  cells.  These  cells  may  be  pigmented  as 

58 


FIBROUS    TISSUE.  59 

seen  in  the  iris  and  choroid.  Within  the  network  thus 
formed  lies  the  intercellular  substance.  In  young  tissue, 
the  cells  are  not  all  of  the  above  form.  Some  are  round, 
others  are  spindle-shaped ;  these  gradually  become  converted 
into  the  stellate  variety. 

The  WANDERING  cell  passes  into  the  tissue  from  the  blood- 
vessels. It  may  return,  or  remain  and  become  a  fixed,  or 
true  connective  tissue  cell. 

PLASMA  cells  are  large,  granular,  fixed  elements,  especially 
noticeable  in  areolar  tissue.  They  are  at  first  oval  or  ob- 
long, and  later  change  to  the  stellate  type. 

The  INTERCELLULAR  substance  is  soft,  and,  in  most 
varieties,  fibrous.  These  fibrils  react  characteristically  to 
certain  stains,  as  will  be  pointed  out  later.  They  vary  in 
thickness,  and  are  arranged  in  bundles  which  may  be  paral- 
lel, or  may  interlace.  These  bundles  lie  in  a  more  or  less 
homogeneous  ground  substance  that  varies  in  quantity  in  the 
different  varieties. 

The  origin  of  the  intercellular  substance  is  still  in  dispute. 
Two  theories  are  advanced.  According  to  some  writers,  it 
is  of  intracellular  origin ,  while  others  claim  it  to  be  inter- 
cellular in  derivation;  in  other  words,  it  is  formed  in  the 
homogeneous,  semi-solid  intercellular  or  ground  substance, 
which  exists  before  the  fibrils  appear.  The  real  origin  is 
probably  by  a  combination  of  these  two  processes.  It 
seems  that  the  intercellular  substance  is  formed  from  the 
peripheral  protoplasm  of  the  cell,  which  becomes  fibrillar 
in  character.  This  small  amount  of  differentiated  proto- 
plasm is  then  supposed  to  increase  itself,  and  so  give  rise 
to  the  remainder  of  the  fibrils. 

The  origin  of  the  elastic  fibres  is  not  so  plain,  both  of  the 
above  views  being  held  in  regard  to  them.  In  elastic  carti- 
lage, they  are  of  intercellular  origin,  but  still  the  intra- 
cellular formation  must  not  be  lost  sight  of. 


6o 


CONNECTIVE    TISSUES. 


b 


FIG.  23. 

A. — Mucous  Connective  Tissue,  a.  Spindle  cells;  5.  stellate  cell;  c.  inter- 
cellular substance.  B. — Cross  Section  of  Tendon,  a.  Epitendineum; 
b.  peritendineum;  c.  tendon  fasciculi;  d.  interfascicular  space.  C. — 
Part  of  B,  highly  magnified,  a.  Epitendineum;  b.  cell  in  a;  c.  peri- 
tendineum; d.  tendon  fasciculus;  e.  interfascicular  space.  D. — Tendon 
Cells  from  Interfascicular  Spaces.  E. — Elastic  Tissue,  Cross-sec- 
tion of  Ligamentum  Nuchae.  a.  Elastic  fibres;  b  white  fibrous 


WHITE    FIBROUS    TISSUE.  6l 

i.  WHITE  FIBROUS  tissue  consists  of  fine  or  coarse 
bundles  of  inelastic  fibrils,  either  parallel  or  forming  a  deli- 
cate mesh  work.  Its  two  subdivisions  are,  a,  loose,  and  b, 
dense. 

a.  Loose  fibrous  connective  tissue  is  a  minute  network 
of  small  bundles  of  fibrils  formed  for  the  support  of  capil- 
lary blood-vessels.      The  fibrils  are  delicate,  less  than   i 
micron  in  diameter,  do  not  branch  or  anastomose  and  are 
held  in  bundles  by  a  small  amount  of  cement  substance. 
The  cellular  elements  are  of  the  types  named  above,  and 
are  few  in  number.     Upon  boiling,  it  yields  gelatin,  is  not, 
or  only  slowly,  digested  by  pancreatin,  and  is  swollen  by 
acetic  acid. 

It  forms  the  capsules  of  organs,  and  is  found  as  the  tu- 
nica propria  and  submucosa  of  the  alimentary  and  respi- 
ratory tracts. 

b.  In  the  dense  variety,  the  fibrils  are  coarser,  and  ar- 
ranged in  larger  bundles,  which  are  usually  parallel. 

TENDONS  are  dense  white  fibrous  tissues,  in  which  all  the 
fibril  bundles  have  a  parallel  course.  The  whole  structure 
is  surrounded  by  a  sheath  of  looser  tissue,  called  the  epi- 
tendineum,  from  the  inner  surface  of  which  septa  are  sent 
in  that  divide  the  tendon  fibres  into  large  secondary  bun- 
dles. These  latter  are  further  subdivided  into  primary 
bundles,  each  of  which  is  surrounded  by  a  minute  sheath, 
the  peritendineum.  Between  the  individual  bundles,  lie 
the  peculiar  tendon  cells.  These  are  flattened,  rectangular 
elements  arranged  end  to  end  upon  the  tendon  bundles. 

supportive  tissue.  F. — E  highly  magnified,  a.  Elastic  fibres;  b.  white 
fibrous  supportive  tissue.  G. — Areolar  Tissue,  a.  White  fibre  bundles; 
b.  elastic  fibres;  c.  spindle  cell;  d.  granule  cell;  e.  plasma  cell;/,  stellate 
cell.  H. — Adipose  Tissue,  a.  Interlobular  connective  tissue;  b.  fat 
cells;  c.  nucleus  and  protoplasm  and  of  the  cell.  I. — H  highly  magni- 
fied, a.  Fat  cell;  b.  protoplasm  and  nucleus  of  cell.  K. — Lymphoid 
Tissue,  a.  Leukocytes;  b.  stellate  connective  tissue  cells;  c.  reticulum. 
L. — Pigmented  Connective  Tissue  Cell  from  a  Pike. 


62  CONNECTIVE    TISSUES. 

The  nuclei  are  peculiarly  arranged.  In  two  adjoining  cells 
they  will  be  seen  near  the  line  of  junction,  but  in  the 
cells  on  either  side  of  these,  they  are  separated  by  nearly 
the  length  of  the  two  cells. 

In  FASCIA  and  the  DURA  the  bundles  are  large,  dense, 
interwoven  and  closely  packed. 

2.  ELASTIC  tissue,  as  its  name  indicates,  has  the  peculiar 
property  of  elasticity. 

The  fibres  are  yellow  in  color,  refractile,  and  coarser  than 
those  of  the  white  variety,  averaging  1-5  microns  in  diame- 
ter. In  AREOLAR  tissue,  they  are  branched,  while  in  other 
places  bands  and  even  membranes  are  formed  (arteries). 
When  separated  and  ruptured,  the  torn  ends  curl.  This 
occurs  in  no  other  tissue.  According  to  Mall,  each  fibre 
consists  of  a  delicate  sheath,  surrounding  the  elastic  sub- 
stance; the  latter  stains  deeply  with  magenta. 

This  variety  occurs  in  the  ligamentum  nuchae,  where  the 
fibres  are  very  heavy,  and  are  surrounded  by  white  inelastic 
fibres,  in  the  ligamentum  subflava,  in  blood-vessels,  and  in 
the  true  skin. 

Elastic  tissue  is  digested  by  pancreatin  and  somewhat  by 
pepsin,  but  not  by  acetic  acid;  upon  boiling  it  yields 
elastin. 

3.  Mucous,   or   EMBRYONIC,    connective    tissue   is    that 
variety  in  which  the  intercellular  substance  is  semi-fluid. 

The  cellular  elements  are  mostly  of  the  spindle-shaped 
variety,  although  numerous  stellate  cells  are  present. 
Round  cells  are  also  frequently  seen. 

The  intercellular  substance  is  semi-solid  in  the  youngest 
tissue,  and  takes  a  peculiar  homogeneous  stain.  As  the 
tissue  becomes  older  fibrils  begin  to  develop,  and  of  these, 
the  white  are  formed  into  bundles,  while  the  elastic  are 
usually  individual. 

Mucous  connective  tissue  is  found  in  the  umbilical  cord, 


RETIFORM    CONNECTIVE    TISSUES.  63 

in  embryos,  in  the  vitreous   humor  of   the  eye  and*  in  the 
pulp  of  the  teeth. 

4.  RETIFORM  connective  tissues,  or  RETICULUM,  is  the 
supportive  tissue  of  glands  and  gland-like  organs.  It  con- 
sists of  delicate  bundles  of  fibrils  forming  a  network,  in 
the  meshes  of  which  are  found  the  functionating  cells  of  the 
organ.  The  cells  are  chiefly  stellate  in  form,  and  their 
processes  anastomose  around  the  fibril  bundles. 


FIG.  24. — INTERMUSCULAR  CONNECTIVE  TISSUE  BUNDLES  OF  MAN. 

a.  Fat  drop;  b.  fat  cells;  c.  bundles  of  white  fibres;  d.  nucleus  of  a  cell;  e. 

elastic  fibres  (Stohr's  Histology}. 

This  tissue  is  more  resistant  to  those  reagents  that  dis- 
solve the  white  variety  (hydrochloric  acid  and  potassium 
hydrate)  and  does  not  yield  elastin  upon  boiling,  but  a 
mixture  of  gelatin  and  reticulin,  nor  is  it  digested  by 
pancreatin. 


64  CONNECTIVE   TISSUES. 

5.  MIXED,  or  AREOLAR,  connective  tissue  is  a  combination 
of  the  white  and  elastic  varieties. 

The  white  tissue  is  present  in  the  form  of  delicate  bundles, 
and  these  form  a  loose  network  with  the  elastic  fibres,  which 
are  usually  thin  and  branched.  The  stellate  and  wandering 
cells  are  well  represented,  but  the  plasma  cells  are  more 
numerous  than  in  any  other  variety  of  tissue. 

This  variety  is  found  binding  the  skin  to  the  fascia  be- 
neath and  between  muscles. 

Modified. — In  these  varieties  of  connective  tissue,  the 
intercellular  substance  varies  from  liquid  (blood)  to  the 
hard,  unyielding  material  found  in  bone  and  dentin. 

The  cellular  elements  also  differ,  as  will  be  seen  when 
each  variety  is  discussed. 

6.  ADIPOSE   tissue,   or  FAT,   is   white  fibrous   tissue,   in 
which  the  cells  have  become  repositories  for  fat  globules. 
These  cells  are  quite  numerous,  but  the  stellate  shape  is  lost. 

The  minute  globules  unite  to  form  a  single  large  drop  that 
distends  the  delicate  cell-membrane.  By  this  coalescence, 
the  protoplasm  and  nucleus  of  the  cell  are  forced  to  one 
side,  and  are  seen  as  a  thin  band,  or  crescent.  The  nucleus 
may  contain  vacuoles. 

Fat  cells  are  spherical,  when  not  closely  packed,  as  the 
fat  is  liquid  at  the  body  temperature.  After  death, 
margarin  crystals  are  seen  in  the  protoplasm.  The  cells  are 
collected  into  groups  called  lobules,  and  these  form  large 
masses  called  lobes.  Blood-vessels,  nerves  and  lymphatics 
are  present  in  considerable  number.  The  first  named  are 
especially  numerous,  as  there  is  a  close  relation  between  fat 
deposition  and  the  vascularity  of  the  part. 

According  to  some  writers,  fat  cells  are  specialized  con- 
nective cells  that  exist  in  no  other  form.  This  seems 
doubtful,  however,  as  experiments  have  shown  that  when 
animals  are  starved,  the  spherical,  fat-containing  cells  re- 


LYMPHOID    TISSUE.  65 

turn  to  the  stellate  form  as  the  fat  is  removed.  Fram  this, 
it  would  seem  that  these  cells  act  merely  as  storage  cells. 

When  adipose  tissue  is  studied,  after  ordinary  prepara- 
tion, merely  a  network  of  fibres  and  cell  boundaries  is  seen. 
This  is  due  to  the  fact  that  the  fat  has  been  removed  by  the 
alcohol  leaving* the  insoluble  white  fibrous  supportive  tissue. 
In  such  sections,  the  nucleated  crescents  of  protoplasm 
are  readily  observable.  In  sections  of  osmicated  fat,  the 
peripheral  cells  are  circular  in  outline,  while  the  deeper 
ones  are  irregular  and  black,  due  to  the  action  of  the  osmic 
acid,  which  is  a  characteristic  reagent  for  fat.  Sudan  III, 
also  used  as  a  test  for  fat,  stains  the  globules  dark  red. 

Adipose  tissue  is  found  widely  distributed  over  the  body, 
except  in  the  penis,  scrotum,  ear  and  eyelid.  From  the 
orbit  and  around  the  kidneys  it  never  entirely  disappears, 
though  death  be  due  to  starvation. 

7.  LYMPHOID  tissue  is  a  special  form  of  the  connective 
variety  consisting  of  a  network  of  reticulum,  in  the  meshes 
of  which  are  found  leukocytes,  or  white  blood-cells. 

These  cells  are  usually  the  small  lymphocytes,  although 
varying  numbers  of  the  large  lymphocytes  (hyalin  cells)  and 
polynuclear  cells  are  to  be  seen.  For  a  description  of  these 
cells,  see  Blood  (p.  107). 

For  readiness  of  comprehension,  LYMPHOID  tissue  is 
divided  into  four  varieties:  a.  DIFFUSE;  b'.  SOLITARY  FOL- 
LICLE; c.  PEYER'S  PATCH,  or  AGMINATED  FOLLICLE;  and  d. 

LYMPH  NODE. 

a.  DIFFUSE  LYMPHOID  tissue  is  an  indefinite  collection  of 
leukocytes  in  an  organ.  The  cells  are  not  especially 
arranged,  neither  is  there  a  special  supportive  tissue  present, 
as  in  the  last  two  varieties. 

It  is  found  in  the  tunica  propria  of  the  alimentary  and 
respiratory  tracts,  and  the  cells  are  merely  scattered  be- 
tween the  bundles  of  white  fibrous  tissue.  It  forms  the 


66  CONNECTIVE   TISSUES. 

medulla  of  the  thymus  body,  and  the  bulk  of  the  tonsil  and 
spleen,  and  is  transient  in  character. 

b.  SOLITARY  FOLLICLES  are  small,  dense  collections  of 
leukocytes  in  white  fibrous  tissue,  as  above.     There  is  no 
special  supportive  tissue  present;  although  the  outline  may 
be  slightly  irregular,  it  is  sharp.     Each  follicle  usually  shows 
a  lighter  center  in  which  the  cells  are  fewer  and  younger. 
This  is  called  the  germinal  center,  and  here  the  new  cells  are 
formed  by  karyokinetic  division. 

Solitary  follicles  are  found  in  the  alimentary  and  respira- 
tory tracts,  the  spleen  and  tonsil.  They,  like  the  diffuse 
variety,  are  transient  structures.  (See  Fig.  41,  page  115.) 

c.  A  PEYER'S  PATCH  is  a  more  or  less  regular  collection 
of  solitary  follicles  sharply  outlined  from  the  surrounding 
tissue.     Each  patch  consists  of  ten  to  sixty  solitary  follicles, 
each  of  which  usually  shows  a  germinal  center.      (See  Fig. 
51,  p.  141). 

Peyer's  patches  are  found  in  the  ileum. 

d.  LYMPH    NODES    (Lymph    Glands)    are    small,    bean- 
shaped  bodies  interposed  in  the  pathways  of  the  lymphatic 
vessels.     As    they   are   closely   related    to    the   Lymphatic 
System,  their  structure  will  be  there  considered. 

8.  The  CARTILAGES  are  characterized  by  a  solid  inter- 
cellular substance.  The  cellular  elements  also  differ  from 
those  previously  cl escribed. 

Three  varieties  are  found  in  man:  the  HYALIN,   WHITE 

FIBRO  and  YELLOW  ELASTIC. 

The  general  structure  will  first  be  considered,  under  />rn- 
chondrium,  cells  and  intercellular  substance. 

The  perichondrium  is  a  fibrous  sheath  that  surrounds 
cartilage  and  gives  rise  to  its  cellular  elements. 

It  is  composed  of  white  fibrous  tissue,  and  is  divided, 
functionally,  into  two  parts.  This  division  is  not  apparent 
under  the  microscope,  as  the  layers  fade  into  each  other. 


CARTILAGE.  67 

The  outer  part  is  the  fibrous  layer,  and  contains  lew  cells. 
The  inner  portion,  or  chondro genetic  layer,  is  rich  in  cells 
that  are  not  of  the  stellate  type,  but  flattened  and  elongated, 
or  spindle-shaped.  These  are  the  chondroblasts,  which 
become  cartilage  cells.  Blood-vessels  also  are  present. 

The  cartilage  cells,  or  chrondroblasts,  vary  in  the  different 
portions  of  the  cartilage.  Just  beneath  the  perichondrium, 
they  are  flat  and  'thin,  indicating  an  early  stage.  Toward 
the  center,  they  gradually  become  broader  until,  finally, 
they  are  oval  or  round  in  form.  Each  cell  is  rich  in  pro- 
toplasm, which  contains  one  or  more  vacuoles.  The 
nucleus  is  usually  prominent.  The  cell  is  sharply  outlined 
from  the  surrounding  substance  by  a  thick  wall,  the  capsule. 
This  is  a  product  of  secretion  of  the  cell,  and  it  is  cast  off, 
as  a  rule,  every  time  the  cell  divides.  Each  cell  may  be 
individual,  or  several  may  be  seen  within  one  capsule, 
which  is  due  to  the  fact  that  the  new  cells  did  not  form 
capsules  for  themselves.  This  is  seen  especially  in  ossi- 
fication of  cartilage.  Between  the  cell  and  the  capsule  is 
usually  a  space  called  the  lacuna. 

The  intercellular  substance  varies.  In  the  HYALIN  variety, 
it  is  apparently  homogeneous;  in  -white  fibro,  it  is  composed 
mainly  of  white  fibrous  tissue,  while  in  the  yellow  fibro  it 
consists  of  yellow  elastic  fibres. 

HYALIN  CARTILAGE  is  a  peculiar  bluish  or  pearly  tissue, 
which  is  elastic,  and  readily  cut  with  a  knife. 

The  cellular  elements  are  as  above.  They  are  quite 
numerous,  and  close  together  just  beneath  the  perichon- 
drium. Further  down,  a  number  are  usually  found  within 
one  lacuna  and  capsule. 

The  intercellular  substance  or  matrix,  is  apparently  homo- 
geneous. Upon  very  careful  study,  and  treatment  with 
special  reagents,  it  shows  a  fibrillar  character,  in  the  meshes 
of  which  is  seen  the  ground  substance,  which  is  homogeneous. 


68  CONNECTIVE   TISSUES. 

This  ground  substance  is  formed  by  a  fusion  of  the  cast-off 
capsules,  and  responds  very  well  to  hematoxylin,  showing 
a  peculiar  bluish  color. 

This  variety  of  cartilage  is  found  covering  articular  sur- 
faces, lining  joint-cavities,  as  the  costal,  tracheal  and  most 


®> 

r    '-£}, 


ABC 

FIG.  25. — SECTIONS  OF  CARTILAGE. 

A. — HYALIN  CARTILAGE,  a.  Fibrous  layer  of  perichondrium;  b.  genetic 
layer  of  perichondrium;  c.  youngest  chondroblasts;  d.  older  chondro- 
blasts;  e.  capsule;  /.  cells;  g.  lacuna.  B. — ELASTIC  CARTILAGE.  C. — 
WHITE  FIBRO-CARTILAGE. 

of  the  laryngeal  cartilages.     It  precedes,  with  a  few  excep- 
tions, all  the  bones  of  the  body,  and  may  ossify  in  old  age. 

WHITE  FIBRO  CARTILAGE  consists  of  islands  of  the  hyalin 
variety,  separated  by  an  intercellular  substance  made  up  of 
delicate  bundles  of  white  fibrous  tissue.  This  form  may 
calcify  or  ossify  in  old  age. 


CARTILAGE.  69 

It  is  not  very  abundant,  and  is  found  deepening  joint- 
cavities,  as  inter-articular  fibro-cartilages,  and  as  the  inter- 
vertebral  discs. 

YELLOW  FIBRO,  or  ELASTIC  CARTILAGE  is  that  variety  in 
which  the  intercellular  substance  is  composed  of  elastic 
fibres. 

It  is  practically  hyalin  cartilage  in  which  the  hyalin 
matrix  has  been  replaced  by  elastic  tissue.  The  cartilage 
cells  are  found  in  small  groups,  surrounded  by  only  a  small 
amount  of  the  hyalin  substance.  This  variety  never 
ossifies  or  calcifies,  and  is  to  be  looked  for  in  regions  where 
elasticity  is  required,  as  in  the  epiglottis,  ear,  Eustachian 
tube  and  small  laryngeal  cartilages. 

Cartilage  contains  no  blood-vessels,  except  in  the  perichon- 
drium,  and  during  the  developing  stage.  Lymph  channels 
are  said  to  be  absent,  so  that  its  nutrition  is  not  of  a  very 
high  order. 

9.  BONE  is  the  most  highly  differentiated  of  the  connect- 
ive tissues.  It  is  characterized  by  the  presence  of  a  very 
hard,  unyielding  intercellular  substance  that  has  a  char- 
acteristic arrangement. 

BONES,  like  cartilage,  are  surrounded  by  a  fibrous 
sheath,  the  periosteum,  beneath  which  is  the  bone  substance 
proper;  the  latter  consists  of  cells  and  intercellular  substance. 

The  periosteum  is  composed  of  two  layers — outer,  or 
fibrous,  and  inner,  or  genetic. 

The  outer  layer  consists  of  white  fibrous  tissue,  support- 
ing a  large  number  of  blood-vessels,  and  containing  but  few 
cells.  The  inner,  or  genetic,  layer  is  rich  in  cells  and  capil- 
laries. These  cells  are  the  future  osteoblasts  that  secrete 
the  osseous  tissue.  From  its  inner  surface,  it  sends  in 
bundles  of  fibres  that  pierce  the  layer  of  bone  at  right 
angles,  and  bind  them  together.  These  are  Sharpey's 
fibres. 


70  CONNECTIVE    TISSUES. 

The  cells  are  all  of  the  irregular  stellate  type,  and  consist 
of  flattened  bodies  and  short  processes  that  extend  into 
small  canals,  to  be  described  later.  The  protoplasm  is  not 
very  abundant,  and  the  nuclei  are  oval,  and  often  vesicular. 

The  intercellular  substance  is  hard  and  resistant.  It  con- 
sists of  osseous  material  that  is  secreted  by  the  cells,  and  is 
peculiarly  arranged  in  the  compact  variety.  It  contains 
spaces,  or  lacuna,  from  which  extend  minute  canals,  or 
canaliculi.  Beside  these,  there  are  a  great  number  of 
canals  that  vary  in  length  and  diameter.  These  are  the 
Haversian  canals. 

BONE  is  composed  of  inorganic  and  organic  salts;  the 
former  are  soluble  in  mineral  acids,  by  which  they  may  be 
removed  and  the  tissue  cut.  The  latter  are  removed  by 
burning,  after  which  process  the  inorganic  substance  re- 
mains as  a  porous  mold  of  the  bone. 

There  are  two  varieties — CANCELLOUS,  or  SPONGY,  and 

COMPACT,  or  SOLID. 

CANCELLOUS  BONE  consists  of  spicules  forming  a  network 
resembling  a  sponge.  These  spicules  have  a  fibrillar 
structure,  and  contain  little  spaces,  called  lacuna.  In  the 
living  condition,  these  lacunae  are  occupied  by  bone-making 
cells,  termed  osteoblasts. 

This  variety  is  found  around  the  medullary  cavity  and  in 
the  heads  of  the  long  bones,  and  forming  the  central  portion 
of  the  flat  bones.  The  meshes  of  the  network  are  covered 
by  the  endosteum  and  are  rilled  with  marrow. 

COMPACT  BONE  has  a  characteristic  structure.  The  os- 
seous matter  is  arranged  in  layers,  or  lamella,  between 
which  lie  the  lacuna.  There  are  four. varieties  of  lamellae: 
a.  Periosteal,  peripheral,  or  circumferential;  b.  Haversian, 
or  concentric;  c.  Intermediate,  ground,  or  irregular;  and  d. 
Perimedullary,  or  Internal. 

a.  The   peripheral,    periosteal,    or   external    lamellae    are 


BjONE.  71 

those  formed  directly  from  the  periosteum.  They  are  few 
in  number,  and  several  are  required  to  complete  the  cir- 
cumference. Between  them  are  a  number  of  irregular 
spaces,  lacunae,  from  which  little  canals  extend,  the  canal- 
iculi.  The  external  layer  has  a  number  of  small  depressions 
called  Howship's  fovece,  or  lacuna.  These  are  occupied  by 
large  bone-destroying  cells  called  osteoclasts.  Haversian 


FIG.  26. — CROSS-SECTION  OF  HUMAN  COMPACT  BONE. 

a.  Periosteum;  b.  peripheral  lamellae;  c.  Haversian  canals;  d.  lacunae;  e. 
interstitial  lamellae;/,  perimedullary  lamelhe;  g.  marrow;  h.  Haversian 
lamellae  (Stb'hr's  Histology}. 


canals  are  not  present,  but  larger  canals,  containing  blood- 
vessels from  the  periosteum,  are  seen.  These  are  Volk- 
mann's  canals. 

b.  The  Haversian  lamellae,  which  are  probably  the  most 
numerous,  are  thin  layers  circularly  arranged  around  a 
small  central  canal  called  the  Haversian  canal.  These 
layers  are  separated  by  the  lacunae,  and  pierced  by  the 
canaliculi.  The  lamellae  of  a  system  are  parallel  to  one 
another,  but  the  different  systems  usually  run  at  various 
angles. 


72  CONNECTIVE    TISSUES. 

An  Haversian  system  consists  of  the  lamellae,  canal, 
lacunae  arid  canaliculi. 

The  canals  are  occupied  by  blood-vessels,  nerves  and 
lymphatics.  Those  nearest  the  marrow  cavity  contain 
marrow.  The  canals  are  generally  parallel  to  the  long 
axis  of  the  bone,  and  anastomose  freely  with  one  another. 

c.  The  intermediate,  interstitial,  or  irregular  lamellae   lie 
between  the  Haversian  system,  and  are  irregular  in  size  and 
form.     They  are  the  remains  of  Haversian  and  periosteal 
lamellae,  altered   by  the  growth  of   the  bone  in  diameter. 
No  canals  are  found   here,  but  lacunae  and  canaliculi  are 
present  between  the  lamellae. 

d.  The  perimedullary,  or  internal,  lamellae  are  not  very 
regular,  and  are  found  surrounding  the  medullary,  or  mar- 
row cavity. 

The  lacuna  are  small,  irregular  spaces  found  between 
the  various  lamellae  throughout  the  bone,  and  occupy  a 
portion  of  each  of  the  adjacent  lamellae,  and  do  not  lie  in 
one  alone.  These  spaces  are  said  to  be  lined  by  a  delicate 
membrane.  They  contain  the  osteoblasts. 

Extending  in  all  directions,  are  small  canals,  or  canalicuh, 
that  communicate  with  those  of  other  lacunae,  so  that  a 
series  of  intercommunicating  spaces  results.  Those  lacunae 
lying  nearest  the  Haversian  canals,  communicate  with 
them,  but  the  peripheral  ones  of  a  system  do  not  com- 
municate, to  any  great  extent,  with  those  of  the  interstitial 
lacunae.  The  canaliculi  serve  as  supports  for  the  processes 
of  the  osteoblasts. 

The  compact  portions  of  the  heads  of  bones  contain  no 
Haversian  systems  and  no  large  lacunae  so  that  pressure 
can  more  readily  be  borne.  Vessels  do  not  enter  the  bone 
here. 

The  MEDULLARY  CAVITY,  which  contains  the  nutrient 
marrow,  is  a  large  space,  in  the  shafts  of  the  long  bones;  it 


BONE-MARROW.  73 

is  lined  by  the  endosteum  which  is  analogous  in  structure 
and  function  to  the  periosteum. 

The  MARROW  is  of  two  varieties,  red  and  yellow.  The  red 
is  found  in  young  persons,  while  the  yellow  occurs  in  those 
above  the  prime  of  life.  The  difference  is  due  to  the  pres- 
ence of  a  great  deal  of  fat  in  the  yellow,  whereby  the  color 
becomes  changed.  It  is  not  a  blood-making  tissue  as  the 
cellular  elements  'are  few  or  may  be  entirely  wanting. 
In  disease,  however,  it  may  again  become  red. 

MARROW  consists  of  a  delicate  network  of  reticulum, 
derived  from  the  endosteum,  supporting  a  close  capillary 
plexus  and  a  number  of  different  cells.  These  cells  are: 

MYELOCYTES,  Or  MARROW  CELLS;  NUCLEATED  RED  BLOOD 
CELLS,  Or  ERYTHROBLASTS,  WHITE  BLOOD  CELLS,  OR  LEUKO- 
CYTES, and  MYELOPLAXES. 

MYELOCYTES  are  large  nucleated  masses  of  granular  pro- 
toplasm. The  nucleus  is  usually  large  and  oval  or  round 
in  shape;  the  chromatin  is  small  in  quantity.  The  proto- 
plasma  contains  fine  granules  that  may  or  may  not  react  to 
acid  stains;  pigment  granules  are  not  infrequently  found. 
These  cells  may  show  ameboid  movements,  and  are  found 
in  the  blood  in  certain  diseases. 

ERYTHROBLASTS,  or  NUCLEATED  RED  CELLS. — These  cells 
differ  from  the  ordinary  red  cells  in  possessing  a  nucleus, 
and  may  show  mitotic  figures.  They  vary  somewhat  in 
size,  but  are  seldom  over  9.5  microns  in  diameter.  By  a 
loss  of  the  nucleus,  these  cells  become  the  erythrocytes,  or 
normal  red  cells. 

The  LEUKOCYTES  are  usually  the  finely  and  coarsely 
granular  eosinophiles,  and  the  bas ophites;  lymphocytes  are 
usually  not  numerous. 

MYELOPLAXES,  or  OSTEOCLASTS,  are  very  large,  irregular 
cells.  The  protoplasm  is  abundant,  and  a  number  of  nuclei 
may  be  seen.  These  cells  are  of  great  importance  in  bone 


74  CONNECTIVE    TISSl  KS. 

destruction,  from  which  the  term  osteoclast  is  derived. 
They  may  be  capable  of  ameboid  movements  and  are 
phagocytic. 

The  functions  of  red  marrow  are  to  make  erythrocytes, 
granular  leukocytes  in  large  numbers  and  to  store  fat. 

Bones  are  nourished  by  blood-vessels  that  enter  through 
the  nutrient  foramen  and  pass  to  the  marrow  cavity. 
From  here,  branches  are  sent  to  the  various  parts  by  way 
of  the  Haversian  canals.  Other  vessels,  derived  from  the 
periosteum,  lie  in  Volkmann's  canals,  which  are  found  in 
the  circumferential  lamellae. 

Nerves  and  lymphatics  accompany  the  blood-vessels. 

Development  of  Bone. — Bone  is  not  a  primary,  but  a 
secondary  tissue.  It  is  preceded  by  cartilage  or  by  fibrous 
tissue.  Bone  developed  from  hyalin  cartilage  is  called 
ENDOCHONDRAL,  while  that  developed  in  fibrous  tissue  is  re- 
ferred to  as  INTRA-MEMBRANOUS  bone. 

ENDOCHONDRAL  bone  formation  is  the  process  by  which 
the  hyalin  cartilage  is  converted  into  SPONGY  bone.  It  is, 
in  reality,  a  combined  process,  for  so  soon  as  the  spongy 
bone  is  formed,  this  is  changed  to  the  compact  variety  by  the 
intra-membranous,  or  periosteal  method. 

When  OSSIFICATION  begins,  the  cartilage  cells  in  that 
vicinity  begin  to  multiply  rapidly,  and  arrange  themselves 
in  rows  parallel  with  the  long  axis  of  the  bone.  Multiplica- 
tion is  most  rapid  in  the  center  of  the  area,  and,  as  a  result, 
the  new  cells  are  unable  to  form  new  capsules  for  themselves ; 
in  consequence,  a  large  number  are  seen  in  one  space  called 
a  primary  areola,  or  marrow  space.  In  the  cartilage  be- 
tween these  spaces,  calcareous  matter  is  deposited,  and  the 
cells  above  and  below  arrange  themselves  into  parallel 
rows.  The  cells  within  the  areolae  either  disappear,  be- 
come osteoblasts,  or  osteoclasts;  the  latter  dissolve  the  car- 
tilaginous and  calcareous  partitions  between  the  spaces. 


BONE    DEVELOPMENT.  75 

As  a  result  of  the  latter,  larger  spaces  are  formed,  and  these 
are  the  secondary  areola.  Those  cells  that  become  osteo- 
blasts,  lay  down  a  thin  layer  of  osseous  tissue  upon  the  re- 
maining partitions,  so  that,  at  first,  these  consists  of  a  core 
of  calcific  material  covered  by  a  thin  veneer  of  true  bone. 
As  the  process  continues,  the  calcareous  matter  is  entirely 
removed  and  is  replaced  by  bone. 

While  these  changes  have  been  in  progress,  the  perichon- 
drium  has  become  the  periosteum,  which  now  forms  osteo- 
blasts.  These,  with  trabeculae  of  the  periosteum  and  blood- 
vessels, pass  inward  toward  the  center  of  ossification,  and 
enter  the  areolae.  This  vascularization  forms  the  first 
marrow.  The  blood-vessels  pass  upward  and  downward 
from  the  center,  following  the  process  of  calcification. 
Gradually,  the  delicate  rod  of  cartilage  is  converted  into  a 
rod  of  spongy  bone.  The  articular  portions  are  separated 
from  the  shaft  by  an  interposed  disc,  the  epiphyseal 
cartilage. 

Periosteal  bone  formation  now  begins.  The  inner  sur- 
face of  the  periosteum  becomes  converted  into  a  thin  layer 
of  osseous  tissue,  and  the  osteoblasts  remain  surrounded  by 
a  small  space  that  is  continued  along  its  processes.  This 
space  and  its  continuations  are  the  lacuna  and  canaliculi. 
As  the  inner  surface  is  changed  to  bone,  the  outer  surface 
has  a  corresponding  amount  added  to  it,  so  that  the  thick- 
ness of  the  periosteum  is  proportionately  the  same. 

With  the  formation  of  periosteal  bone,  the  various 
lamella  are  formed.  The  peripheral  are  merely  the  con- 
verted periosteum.  The  Haversian  system  and  lamella 
are  formed  in  the  following  manner.  From  the  inner  sur- 
face of  the  periosteal  layer,  projections  are  formed  at 
various  angles.  These  meet  other  projections,  thereby 
enclosing  a  small  space,  the  primitive  Haversian  canal. 
Osteoclasts  gain  access  and  make  this  space  regular  and 


76 


CONNECTIVE    TISSUES. 


larger.     Then    osteoblasts   lay   down    layer    upon   layer   of 
osseous  matter  until  only  a  small  channel,  the  Haversian 


FIG.  27. — CROSS-SECTION  OF  A  DEVELOPING  BONE  OF  A  HUMAN  FETUS  OF 
FOUR  MONTHS. 

a.  Periosteum;  b.  boundary  between  endochondral  and  periosteal  bone; 
c.  perichondral  bone;  d.  remains  of  area  of  calcification;  e.  endochondral 
bone;  f,  F.  blood-vessel;  g.  gf.  developing  Ha versian  spaces;  h.  marrow; 
i.  blood-vessel  (Stohr's  Histology}. 

canal,  is  left.  The  remains  of  the  peripheral  lamellae  be- 
tween the  various  systems  go  to  make  up  the  interstitial 
lamella. 


BONE    DEVELOPMENT.  77 

With  the  formation  of  the  peripheral  lamellae,* ^.he  net- 
work of  spongy  bone  is  removed  from  the  center  by  osteo- 
clasts.  This  leads  to  the  formation  of  a  marrow  cavity.  As 
the  bone  increases  in  size,  the  cavity  increases  in  proportion, 
by  the  destruction  of  the  surrounding  bone.  During  the 
prime  of  life,  bone  formation  exceeds  cavity  formation,  but 
in  old  age,  the  reverse  is  the  case,  so  that  the  shaft  becomes 
thinner,  and  the  cavity  larger. 

The  bone  increases  in  diameter  by  the  continued  addition 
of  peripheral  lamellae,  as  a  tree  grows  in  thickness.  It 
grows  in  length  by  the  interposition  of  a  disc  of  cartilage 
between  the  shaft  and  head  of  the  bone.  In  this  disc,  new 
cartilage  is  formed  as  rapidly  as  ossification  occurs.  This 
is  the  cambium  layer,  and  should  it  ossify,  that  end  of  the 
bone  would  no  longer  increase  in  length.  This  change 
occurs  normally  when  full  height  is  reached. 

This  method  of  bone  formation  occurs  in  all  bones  except 
those  of  the  face  and  of  the  vault  of  the  cranium. 

Intra-membranous  bone  formation  is  the  process  whereby 
white  fibrous  tissue  becomes  converted  directly  into  bone. 
Two  periosteal  layers  are  present,  and  between  these,  the 
bone  is  formed.  Upon  the  fibrous  bundles  connecting 
them,  osteoblasts  deposit  osseous  material  until  all  are  con- 
verted at  the  same  time  the  formation  of  Haversian  systems 
occurs. 

Such  bones  increase,  in  thickness,  as  above,  and  laterally, 
by  the  maintenance  of  a  layer  of  fibrous  tissue  at  their 
edges.  This  is  the  cambium  layer,  and  when  full  growth  is 
attained,  this  layer  ossifies,  and  union  occurs  between  the 
various  bones. 

10.   DENTIN  will  be  considered  under  the  TEETH. 
•  -II.   BLOOD  is  the  only  liquid  connective  tissue.     As  it  is 
part  of  the  CIRCULATORY  SYSTEM,  it  will  be  considered  when 
that  is  described. 


CHAPTER  V. 


MUSCLE    TISSUES. 

Muscle  tissues  are  those  which  produce  the  various 
movements  of  the  body,  whether  voluntary  or  involuntary. 

Like  epithelial  tissues,  they  consist  chiefly  of  cellular 
elements,  the  intercellular  substance  being  small  in  amount. 
The  varieties  are  voluntary  striated,  involuntary  non- 
striated  and  involuntary  striated. 

Voluntary  striated  muscles  are  characterized  by  being 
under  the  control  of  the  will  and  are  called  skeletal 
muscles.  Each  MUSCLE  consists  of  a  large  number  of  units 
called  fibres,  bound  together  by  white  fibrous  tissue. 

Each  fibre,  or  cell,  is  a  long,  narrow  cylinder.  It  varies 
from  one  to  five  inches  in  length,  and  exhibits  cross  and 
longitudinal  striations.  It  is  composed  of  a  large  number 
of  fibril  I  <z,  which  are  bound  together  by  a  membrane  called 
sarcolemma,  and  separated  from  one  another  by  sarcoplasm. 
Many  peripherally  located  nuclei  are  present. 

Thefibrillcz  consist  of  sarcous  elements  which  stain  darkly 
and  are  doubly  refractile,  or  anisotropic.  The  sarcoplasm 
is  a  palely  staining,  semi-solid  substance  that  lies  between 
the  fibrillae,  and  is  slightly  refractile,  or  isotropic. 

The  longitudinal  striations  are  formed  by  the  alteration  of 
the  fibrillae  and  the  sarcoplasm,  and  are  usually  not  as  dis- 
tinct as  the  cross,  though  at  times  the  reverse  is  the  case. 
The  cross  striations  are  due  to  the  alternation  of  light  and 
dark  discs,  or  bands.  The  dark  bands,  or  Bruecker's  lines, 
are  composed  of  rows  of  parallel  sarcous  elements,  separated 
by  the  sarcoplasm.  These  sarcous  elements  are  cylindric 
except  at  the  ends,  where  they  are  cone-shaped.  The 

78 


VOLUNTARY    MUSCLE.  79 

ends  form  part  of  the  light  disc.  Each  dim  band  is  divided 
transversely  by  a  less  refractile  line,  called  Henseris  disc. 

The  light  discs  are  subdivided  into  three  portions,  an 
intermediate  and  two  lateral.  The  intermediate  disc  consists 
of  a  single  row  of  small  globules,  interposed  between  the 
apices  of  the  cones.  These  are  Dobie's  globules,  or  the 
membrane  of  Krause.  The  lateral  disc  are  merely  the  cone- 
shaped  continuations  of  the  sarcous  elements.  They  are  a 
little  dimmer  than  the  intermediate  disc.  It  will  be  seen 
from  the  figure  that  the  main  portion  of  this  light  disc  con- 
sists of  the  refractile  sarcoplasm. 

The  nuclei  are  numerous,  and  are  found  beneath  the  sar- 
colemma,  but  external  to  the  muscle  substance.  They  are 
long  and  rather  narrow,  but  respond  well  to  the  stain.  In 
some  animals  the  nuclei  lie  in  depressions  in  the  fibres. 

The  SARCOLEMMA  is  a  delicate  fibrous  sheath  that  lies 
close  to  the  fibre.  It  is  not  seen,  as  a  rule,  except  by 
special  preparation.  If  a  fresh  muscle  fibre  be  treated 
with  water,  the  muscle  substance  ruptures,  and  the  delicate 
membrane  is  shown  spanning  the  interval. 

Upon  cross-section,  the  fibres  show  a  sharp  outline,  and 
the  peripheral  nuclei  are  readily  distinguished.  Upon  care- 
ful observation,  the  fibrillae  are  seen  collected  into  groups, 
constituting  Cohnheim's  fields. 

There  are  two  kinds  of  fibres,  white  and  red.  The  white 
predominate  in  man  and  are  poor  in  sarcoplasm.  The  red 
are  rich  in  sarcoplasm  and  the  nuclei  are  deeply  placed.  The 
red  is  intermediate  between  myoplasm  and  the  white  fibres, 
and  in  some  animals  (rabbit)  they  form  whole  muscles.  The 
trapezius  muscle  of  man  contains  both  red  and  white  fibres. 

Contractility  is  an  inherent  quality  of  the  sarcous  elements, 
but  the  sarcoplasm  does  not  possess  it.  Occasionally,  among 
the  tongue  muscles  are  found  some  fibres  that  branch.  Such 
fibres  are  numerous  in  the  tongue  of  the  frog. 


8o 


MUSCLE    TISSUES. 


A. — Longitudinal  section  of  smooth  muscle  fibres — a.  muscle  fibre;  b. 
nucleus;  c.  fibrous  tissue  between  fibres.  B. — Cross-section  of  smooth 
muscle  fibres — a.  perimysial  connective  tissue;  b.  blood-vessel;  c. 
nucleated  fibre;  d.  nonnucleated  fibre.  C. — Longitudinal  section  of 
voluntary  muscle  fibres. — a.  sarcolemma;  b.  nucleus;  c.  end  of  muscle 
fibre;  d.  dark  bands;  e.  intermediate  disc;  /.  nucleus;  g.  lateral  disc. 
D. — Diagrammatic  section  of  cross  and  long  striations — a.  dark  disc; 
b.  lateral  discs;  c.  intermediate  disc.  E. — Cross  section  of  voluntary 
muscle — a.  perimysium;  b.  endomysium;  c.  nucleus  of  perimysium;  d. 
fibrillae;  e.  nucleus  of  muscle;/,  sarcolemma.  F. — Longitudinal  section 
of  cardiac  muscle  fibres — a.  muscle  fibre;  b.  nucleus;  c.  branch.  G. — 
Cross  section  of  cardiac  muscle  fibres — a.  perimysial  sheath;  b.  nucleus 
of  sheath;  c.  muscle  fibre;  d.  nucleus;  e.  radial  plates  of  fibrillae. 


SMOOTH    MUSCLE.  8 1 

Muscles, — Fibres  are  collected  into  definite  groups  called 
Muscles.  Each  muscle  is  surrounded  by  a  sheath  of  white 
fibrous  tissue  called  the  EPIMYSIUM.  From  its  inner  sur- 
face, septa  are  sent  in  that  divide  the  muscle  into  a  number 
of  large  secondary  bundles.  These  secondary  bundles  are 
further  subdivided  into  primary  bundles,  or  fasciculi, 
which  are  invested  by  a  sheath,  the  PERIMYSIUM.  This 
sends  in  fibres  that  pass  between  the  individual  fibres,  and 
these  represent  the  ENDOMYSIUM.  Where  the  muscle  joins 
the  tendon,  the  nuclei  are  especially  numerous. 

The  blood-vessels  pierce  the  epimysium  and  form  branches 
that  follow  the  larger  septa  and  ultimately  reach  the 
perimysium,  where  smaller  branches  are  formed.  These 
pierce  the  perimysium,  and  form  longitudinal  capillary 
meshes,  which  anastomose  and  at  intervals  show  peculiar 
dilatations. 

Lymphatics  are  usually  not  numerous,  and  may  even  be 
wanting. 

The  nerves  follow  the  blood-vessels,  but  the  exact  method 
of  termination  will  be  considered  under  Nerve  Endings. 

Voluntary  striated  muscles  are  found  as  the  skeletal  and 
external  ocular  muscles,  in  the  tongue,  pharynx,  upper  part 
of  the  esophagus,  anus,  diaphragm,  and  in  the  external 
ear  and  larynx. 

The  Involuntary  Nonstriated,  Smooth,  or  Visceral  muscle 
is  not  under  the  control  of  the  will. 

The  individual  fibres  are  short,  narrow  and  spindle- 
shaped.  Each  is  surrounded  by  a  delicate  sheath  which, 
however,  is  not  a  sarcolemma. 

Longitudinal  striations  are  usually  found,  and  these  are 
due  to  the  presence  of  coarse  fibrillae  at  the  periphery  of 
the  fiber. 

In  each  fibre  there  is  but  one  nucleus,  which  is  long, 
slender,  darkly  staining  and  centrally  located.  This  is  not 
6 


82  MUSCLE    TISSUES. 

seen  in  all  cross-sections,  but  when  present,  shows  as  a 
small,  dark  dot.  Branched  fibres  have  been  found  in  the 
aorta  and  bladder  muscle. 

These  fibres  vary  in  length  from  25  to  200  microns,  ordi- 
narily, but  in  the  gravid  uterus  may  attain  a  length  of  600 
microns.  In  diameter,  they  average  about  5  to  7  microns. 

The  fibres  are  arranged  in  bundles  like  the  above,  but  in- 
stead of  forming  masses  like  muscles,  the  bundles  are  ar- 
ranged into  layers,  which  extend  circularly  and  longitudi- 
nally, in  the  hollow  viscera. 

Capillaries  exist  between  the  fibres  as  above. 

The  nerves  are  chiefly  of  the  sympathetic  variety. 

Nonstriated  muscles  are  found  in  the  alimentary  tract 
from  the  middle  third  of  the  esophagus  to  the  anus,  in  the 
ducts  of  glands,  in  the  trachea  and  bronchial  tubes,  within 
the  eyeball,  the  internal  urinary  and  genital  systems  , circu- 
latory (except  the  heart)  and  lymphatic  systems,  and  the 
capsules  of  some  organs. 

Involuntary  Striated,  Cardiac,  or  Branched  Muscle  is  that 
variety  found  in  the  heart. 

The  fibres  are  short,  stubby  cylinders,  possessing  stria- 
tions  but  no  sarcolemma,  although  a  delicate  investing 
sheath  is  present.  These  fibres  vary  from  100  to  200 
microns  in  length,  and  25  to  40  microns  in  breadth. 

A  single  large,  oval,  centrally  placed  nucleus  is  also  pres- 
ent; this  is  usually  surrounded  by  a  zone  of  peculiar,  un- 
differentiated  protoplasm,  in  which  pigment  granules  may 
be  found.  These  pigment  granules  are  numerous  and 
constant  in  certain  diseases  of  the  heart  muscle.  Some- 
times there  are  two  nuclei. 

The  transverse  striations  are  usually  fainter  than  the 
longitudinal. 

A  peculiarity  of  this  variety  is  that  the  fibres  branch. 
These  branches  are  short  and  narrower  than  the  cell-body, 


CARDIAC    MUSCLE.  83 

and  anastomose  with  the  branches  of  other  cells,  fkus  form- 
ing a  syncytium. 

In  cross-sections,  the  fibrillae  are  seen  to  be  particularly 
arranged.  They  are  formed  into  radial  plates  that  start 
from  the  center  or  the  zone  of  undifferentiated  protoplasm 
that  surrounds  the  nucleus. 

The  blood-vessels  enter  into  intimate  relation  with  the 
fibres,  and  are  derived  from  the  coronary  arteries,  the 
smaller  branches  of  which  lie  between  the  muscle  bundles. 
The  capillaries  pass  into  these  and  run  parallel  to  the 
fibres,  in  which  they  often  lie  in  grooves,  and  are  frequently 
seen  within  the  fibre,  surrounded  by  the  muscle  substance. 

The  nerves  are  both  sympathetic  and  cerebro  spinal. 
Sympathetic  ganglia  are  also  present. 

The  following  table  will  give  the  various  characteristics 
of  the  muscle  tissues  in  comparison. 


CHARACTERISTIC. 

VOLUNTARY 
STRIATED. 

SMOOTH. 

1 

CARDIAC. 

Shape. 

Long  cylinder. 

Spindle. 

Stubby 

cylinder. 

Length. 

1-5  inches. 

25—200 

100—  200  microns. 

Nucleus. 

microns. 

Number. 

Many. 

One. 

One. 

Location. 

Peripheral. 

Central.    ; 

Central 

Shape. 

Intermediate. 

Rod. 

Oval. 

Striations. 

Cross  and  long. 

(Longi- 

Cross and  long. 

tudinal 

occasion- 

ally.) 

Sarcolemma. 

Present. 

None. 

None. 

Branches. 

Occasional. 

(Occa- 

Always 

sional.) 

Arrangement. 

In  masses  called 

In  layers. 

As  a  syncytium. 

muscles. 

Control. 

By  will. 

Not    by 

Not  by 

will. 

will. 

CHAPTER  VI. 


NERVE  TISSUES. 

The  Nerve  Tissues  are  the  most  highly  differentiated 
of  all  the  tissues. 

There  are  two  varieties,  gray  and  white.  The  gray  is 
characterized  by  a  grayish  color,  and,  in  the  central  nerve 
system,  is  divided  into  layers.  In  the  spinal  cord  and 
ganglia,  its  arrangement  is  different.  It  consists  of  CELLS 
and  their  processes  and  INTERCELLULAR  SUBSTANCE,  the 
latter  which  is  called  the  NEUROGLIA,  or  SUPPORTIVE  SUB- 
STANCE; myelinated  and  amyelinated  nerve  fibres  are  also 
present. 

A  typic  nerve  cell  consists  of  a  cell-body,  from  which  a 
number  of  processes  extend,  a  nucleus  and  nucleolus.  The 
whole  structure  is  also  called  a  neuron. 

The  cell-body  consists  of  granular  and  fibrillar  protoplasm, 
which  at  the  point  of  origin  of  the  main  process  is  formed 
into  a  mass,  the  axis  cylinder  hillock.  The  fibrillae  are  called 
neurofibrils,  are  seen  only  after  careful  preparation  ac- 
cording to  Golgi's  method,  and  require  a  high  magnification. 
Some  fibrillae  seem  to  be  connected  with  the  cells,  while 
others  apparently  pass  right  through  the  cell-body.  Be- 
sides the  usual  granules  some  very  large  darkly  staining 
bodies  are  seen  in  the  vicinity  of  the  nucleus.  These  are 
the  corpuscles  of  Nissl,  or  the  tigroid  bodies.  The  nucleus 
is  usually  large  and  vesicular  while  the  nucleolus,  also 
large,  stains  very  darkly  and  is  quite  prominent.  Cells 
vary  from  5  to  130  microns  in  diameter. 

The  processes  are  of  two  varieties,  axis  cylinder  and  den- 


NERVE    CELLS.  85 

dritic.  The  axis  cylinder,  neurit,  or  axone,  is  *the  main 
and  largest  process.  It  forms  the  means  of  communication 
between  the  cells  of  an  area  or  those  in  different  regions. 
It  arises  at  the  hillock  and  consists  of  fibrillated  protoplasm. 
There  is  usually  but  one  to  each  cell,  but  some  cells  with 
two  and  more  axones  have  been  found.  Axones  give  off 
branches,  at  right  angle,  called  collaterals,  except  the  cells 
of  the  spinal  ganglia.  These  may  or  may  not  be  myelinated. 
How  these  processes  terminate  will  be  considered  later. 

The  dendriles  are  the  delicate  secondary  processes  of  a  nerve 
cell.  The  number  of  these  processes,  in  reality,  gives  us  the 
basis  of  the  classification  according  to  structure.  As  they 
leave  the  cell-body  they  dwindle  rapidly  in  diameter;  this  is 
due  to  their  prolific  branching.  These  smaller  divisions  are 
the  teledendrites  and  serve  to  bring  the  cell-body  in 
physiologic  relation  with  other  cells.  These  processes  are 
usually  amyelinic  and  do  not  leave  the  gray  substance.  In 
the  case  of  the  cells  of  the  ganglia  of  the  spinal,  cranial 
and  special  sense  nerves  (sensor  cells),  the  peripheral  process, 
called  usually  a  nerve  fibre,  is  in  reality  the  myelinated 
dendritic  process.  The  axone  grows  into  the  central 
system  from  the  ganglion. 

Nerve  cells  are  classified  as  to  i,  Structure,  2,  Type. 

There  are  three  varieties  of  cells  according  to  Structure, 
or  number  of  processes:  UNIPOLAR,  BIPOLAR  and  MULTI- 
POLAR. 

The  UNIPOLAR  CELLS  are  those  possessing  but  one  process. 
In  the  early  embryonal  condition  two  were  in  reality  present 
but  the  growth  of  the  cell  was  such  that  the  two  were 
thrown  together  as  one.  The  individuality  of  each  portion, 
however,  is  retained.  These  cells  occur  in  the  spinal 
ganglia. 

The  BIPOLAR  CELLS  are  those  having  two  processes.  The 
dendritic  process  very  rapidly  breaks  up  into  a  great  number 


86  NERVE   TISSUES. 

of  smaller  ones  called  telodendrites.  This  variety  is  found  in 
the  cerebellum  and  peripheral  sensor  system  (special 
senses) . 

The  MULTIPOLAR  CELLS  which  are  the  most  numerous, 
have  three,  or  more,  processes.  They  are  found  in  the  cere- 
brum, cerebellum  and  spinal  cord. 

Types. — There  are  two  types  of  cells  according  to  the 
course  of  the  axis  cylinder.  In  CELLS  OF  THE  FIRST  TYPE 
(DEITER'S  CELLS)  the  axis  cylinder  leaves  the  gray  substance 
to  become  a  myelinated  nerve  fibre.  In  the  SECOND  TYPE 
(GoLGi's  CELLS)  the  axis  cylinder  never  leaves  the  gray 
substance. 

The  NEUROGLIA  is  the  distinctive  supportive  structure  of 
the  nerve  system.  It  is  not  connective  tissue.  Unlike  the 
intercellular  substances  elsewhere,  it  is  not  the  result  of  the 
secretion  of  the  functionating  cells  (nerve  cells)  but  is  formed 
by  special  cells  called  neuroglia,  or  glia  cells.  These  cells 
secrete  the  intercellular  substance  of  the  neuroglia. 

The  glia  cells,  or  astrocytes,  are  of  two  varieties,  spider  and 
mossy. 

The  spider  cells  possess  small  bodies  which  send  out 
many  thick  branches  varying  in  length.  They  are  found 
in  the  white  substance  and  their  processes  interlace  to 
form  a  supportive  network  for  the  nerve  fibres.  They  are 
the  more  numerous. 

Mossy  cells  possess  larger  cell-bodies  but  shorter  proc- 
esses that  are  finer  and  more  branched.  They  occur 
chiefly  in  the  gray  substance. 

In  addition  to  the  above  a  small  amount  of  connective 
tissue  is  found  in  the  gray  substance.  This  penetrates 
with  the  blood-vessels. 

The  gray  substance  is  found  in  the  cerebrum,  cerebellum, 
pons,  oblongata,  spinal  cord  and  ganglia. 

The  White  substance  consists  of  myelinated  nerve  fibres 


NERVE    CELLS    AND    FIBRES.  87 

bound   together  by  neuroglia  and  connective   tissue,    the 
latter  of  which  supports  the  blood-vessels  chiefly. 

Nerve  Fibres,  the  continuations  of  cells  of  the  first  type, 
are  of  two  varieties,  Myelinated  and  Amyelinated. 

Myelinated,  or  Medullated,  nerve  fibres  have  a  character- 
istic structure.  Each  consists  of  an  AXIS  CYLINDER  that 
lies  in  the  center  and  represents  the  cell  and  shows  a 
fibrillated  structure  somewhat  like  that  of  a  muscle  fibre 
The  fibrillae  are  separated  by  a  pale,  homogeneous  substance 
that  does  not  respond  to  ordinary  stains  and  is  called  the 
neuroplasm.  This  axis  cylinder  is  surrounded  by  a  delicate 
membrane,  the  axilemma. 

The  MYELIN  or  MEDULLARY  SHEATH,  or  WHITE  SUB- 
STANCE of  SCHWANN,  surrounds  the  axis  cylinder.  It  con- 
sists of  a  fine  network  of  kerato-hyalin  containing  in  its 
meshes  a  fatty  substance,  the  myelin.  The  latter  is  black- 
ened by  osmic  acid. 

The  NEURILEMMA,  or  SHEATH  OF  SCHWANN,  is  a  tender 
covering  that  enfolds  the  individual  nerve  fibre.  Not  all 
myelinated  nerve  fibres  possess  neurilemmae,  as  the  fibres 
of  the  optic  and  olfactory  nerves,  of  the  spinal  cord  and 
brain  mass  are  devoid  of  this  sheath. 

At  regular  intervals  are  annular  constrictions,  where  the 
neurilemma  dips  and  touches  the  axis  cylinder.  These 
places  are  the  nodes  of  Ranvier,  and  at  such  points  the  axis 
cylinder  may  give  off  branches  called  collaterals.  The 
portion  between  the  nodes  is  an  internode;  each  contains  a 
nucleus.  In  the  internodes,  funnel-shaped  depressions,  the 
clefts  of  Lantermann,  are  seen. 

Nerve  fibres  are  motor  or  centrifugal  or  efferent  on  the  one 
hand  and  sensor,  centripetal,  or  afferent  on  the  other.  Those 
sensor  fibres  found  peripheral  to  the  ganglia  are  in 'reality 
myelinated  dendrites  and  not  axones,  as  is  usually  stated. 
They  vary  from  2  to  20  microns  in  diameter. 


88 


NERVE    TISSUES. 


FIG.  29. 

A.  Multipolar  cell  from  cerebral  cortex;  B.  multipolar  cell  from  spinal  cord; 
C.  pyramidal  cell  from  cerebral  cortex;  D.  unipolar  cell;  E.  bipolar 
cell;  F.  cell  of  Purkinje,  antler  cell;  G.  mossy  cell;  H.  spider  cell;  I.  cell 
from  spinal  cord  of  an  ox,  showing  pigment  granules;  K.  ganglion;  L. 
sympathetic  or  amyelinated  fibres;  M.  longitudinal  section  of  myelinated 
nerve  fibre — a.  neurilemma;  b.  myelin  sheath;  c.  axis  cylinder;  d.  node 
of  Ranvier;  e.  nucleus;  N.  cross-section  of  osmicated  nerve  fibres;  O.- 
myelinated  nerve  fibre  of  a  guinea-pig  showing  the  reticulum;  P.  mye- 
linated nerve  fibres  of  a  toad,  showing  reticulum  (kerato-hyalin) ;  R. 
motor  neuron,  showing  nerve  cell,  dendrites,  axis  cylinder  and  ending 
of  latter  in  a  muscle;  S.  cross-section  of  nerve  trunk. 


GANGLIA.  89 

An  Amyelinated,  or  Nonmedullated,  nerve  fibre  is  one  that 
possesses  no  myelin  sheath.  It  is  merely  a  naked,  axis 
cylinder  surrounded  by  its  axilemma.  All  the  sympathetic 
fibres  are  of  this  variety  but  some  are  found  in  the  cerebro- 
spinal  system. 

A  Nerve  is  a  collection  of  nerve  fibres  arranged  in  a  defi- 
nite manner. 

Each  Nerve  is  surrounded  by  a  sheath  of  white  fibrous  tis- 
sue, the  EPINEURIUM.  From  this,  septa  pass  inward  and 
divide  the  nerve  into  large  secondary  bundles  that  are 
further  subdivided  into  primary  bundles,  or  fasciculi,  each  of 
which  is  surrounded  by  the  PERINEURIUM.  The  fibres 
contained  in  the  fasciculi  are  separated  from  one  another 
by  the  ENDONEURIUM,  which  is  a  continuation  of  the 
perineurium. 

The  blood-vessels  pierce  the  epineurium  and  branches  are 
sent  along  the  septa  into  the  primary  bundles.  Here 
capillaries  are  formed,  which  run  parallel  to  the  fibres. 
These  vessels  are  the  vasa  nervorum. 

Ganglia  are  collections  of  gray  substance  and  are  found  in 
the  cerebrum,  as  the  basal  ganglia;  in  the  sympathetic 
system,  as  the  sympathetic  ganglia;  and,  within  the  interver- 
tebral  foramina,  as  the  spinal  ganglia. 

A  Ganglion  consists  of  a  limiting  sheath,  or  CAPSULE  of 
white  fibrous  tissue  within  which  the  nerve,  or  ganglion 
cells  are  found. 

The  ganglion  cell  is  a  large  spherical  element  surrounded 
by  a  distinct  space  (lymph  space)  lined  by  endothelial  cells, 
and  consists  of  granular  protoplasm  containing  a  large, 
palely  staining  nucleus,  and  a  distinct  nucleolus.  It  is 
usually  of  the  unipolar  variety.  Between  these  cells  are 
seen  myelinated  and  amyelinated  nerve  fibres,  and  con- 
nective tissue  containing  blood-vessels  and  lymphatics. 

Nerve  Organs  are  of  two  varieties,   i,  Sensor,  or  Nerve 


90  NERVE    TISSUES. 

Beginnings,  and  Motor,  or  Nerve  Endings,  considering  them 
from  a  physiologic  or  functional  standpoint. 

The  Sensor  Organs  are  FREE,  TACTILE  CELLS  and  COR- 
PUSCLES. 

FREE  BEGINNINGS  are  found  in  mucous  membranes,  espe- 
cially in  stratified  epithelium.  The  nerve  fibres  apparently 
reach  the  basement  membrane,  and  upon  piercing  this  lose 
the  neurilemma  and  myelin  sheath.  These  branches  then 
divide  repeatedly  between  the  epithelial  cells. 


FIG.  30. — VERTICAL  SECTION  OF  SKIN  OF  GREAT  TOE  OF  A  MAX. 
A.  Epidermis;  B.  derma;  a.  tactile  cell;  b.  tactile  meniscus;  c.  nerve  fibre; 
d.  connective  tissue  sheath   of  same;  x.  tactile  cells  in  derma  (Stohr's 
Histology}. 

TACTILE  CELLS  are  simple  and  compound. 

The  simple  variety  consists  of  a  disc-like  structure,  6  to  12 
microns  in  size,  which  lies  within  the  epithelial  layer. 
From  this  disc,  or  meniscus,  passes  a  naked  axis  cylinder, 
and  upon  the  disc  lies  the  tactile  cell  which  is  a  mass  of 
granular  protoplasm. 

Compound  tactile  cells  consist  of  two  or  more  discs  con- 
taining between  them  the  tactile  cells.  A  branch  of  a 
myelinated  nerve  fibre  passes  from  each  cell.  These  struc- 
tures are  usually  15  by  30  microns  in  size. 

Tactile  Corpuscles,  or  Bulbs  are  the  most  differentiated 
of  these  organs.  They  vary  in  complexity  from  the  com- 


TACTILE    CORPUSCLES.  9! 

paratively  simple  GENITAL  and  CONJUNCTIVAL  CORPUSCLES 
to  the  CORPUSCLES  OF  MEISSNER  AND  VATER. 

The  GENITAL  and  CONJUNCTIVAL  CORPUSCLES  are  spheri- 
cal bodies  in  which  the  cells  are  not  regularly  arranged. 
The  nerve  fibres  begin  probably  between  the  cells.  These 
organs  average  from  60  to  400  microns  in  length  and  may 
have  as  many  as  ten  nerve  fibres  connected  with  one. 

The  CORPUSCLE  *OF  MEISSNER  is  a  complex  structure  in 
which  the  individual  cells  cannot  be  distinctly  seen.  It  is 


FIG.  31. — CORPUSCLE  OF  MEISSNER  FROM  GREAT  TOE  OF  MAN. 

n.  Myelinated  nerve  fibre;  h.  connective  tissue  sheath;  e.  varicosities.     The 

nuclei  are  invisible  (Stohr's  Histology}. 

surrounded  by  a  sheath  that  encloses  a  number  of  trans- 
versely placed  nuclei.  One  or  more  nerve  fibres  is  con- 
nected with  each  corpuscle,  and  upon  contact  with  the 
corpuscle  the  neurilemma  is  lost.  The  myelin  sheath 
soon  follows  and  the  axis  cylinders,  after  a  spiral  course  are 
thought  to  connect  with  the  end  discs  or  menisci.  These 
bodies  measure  35  to  50  microns  by  45  to  100  and  are  found 
in  the  papillae  of  the  palmar  and  plantar  surfaces  of  the  true 
skin. 

CORPUSCLES  OF  VATER,  or  PACINIAN  BODIES  have  a  very 
definite  structure.  Each  consists  of  a  CAPSULE,  INNER 
BULB  and  KNOB.  The  CAPSULE  consists  of  lamellae,  of  con- 


Q2  NERVE    TISSUES. 

nective  tissue  concentrically  arranged,  which  are  usually 
bound  together  by  an  intracapsular  ligament.  The  layers 
are  covered  by  endothelial  cells  and  represent  so  many 
lymph  spaces. 

The  INNER  BULB  is  an  elongated  cylindric  mass  of  granu- 
lar protoplasm  that  is  connected  with  the  axis  cylinder  of 
the  nerve. 


FIG.  32. — PACINIAN  BODY  FROM  MESENTERY  OF  A  CAT. 

i.  Fat  cells;   2.  artery;  3.    nerve  fibre;    4.    inner    bulb;    5.    axis  cylinder; 

6.  layers  of  the  capsule  (Stohr's  Histology). 

As  the  nerve  meets  the  capsule  the  neurilemma  is  lost. 
When  it  reaches  the  inner  bulb  the  myelin  sheath  disap- 
pears and  the  naked  dendrite  continues  through  the  inner 
bulb  and  ends  in  a  club-like  mass,  the  KNOB. 

These  corpuscles  occur  in  the  derma,  near  joints,  in  the 
mesentery  (especially  in  lower  animals)  and  along  tendons. 

Neuromuscular  Organs. — These  organs  are  spindle- 
shaped,  and  consist  of  4  to  20  small  voluntary  muscle 
fibres,  the  inlra-fusal  fibres,  surrounded  by  a  delicate  white 


TENDON-SPINDLES. 


93 


fibrous  sheath,  the  axial  sheath.  External  to  triis  is  the 
capsule  composed  of  about  six  layers  of  white  fibrous  con- 
nective tissue  concentrically  arranged  and  separated  from 
the  axial  sheath  by  a  lymph  space. 

In  the  equatorial  region  of  the  organ  the  muscle  fibres 
consist  chiefly  of  sarcoplasm  and  the  striations  are  faint, 
while  at  the  ends  the  striations  are  quite  distinct. 


FIG.  33. — TENDON-SPINDLE  OF  A  CAT. 

a.  Myelinated  nerve  fibre;  b.  tendon  bundle;  c.  muscle  fibres;  d.  terminal 
ramifications  (Stohr's  Histology). 

Each  fibre  arises  as  a  small  bulb-like  knob  and  then 
winds  around  the  intrafusal  muscle  fibres.  As  the  axial 
sheaths  are  reached  each  branch  becomes  myelinated. 
The  various  fibres,  representing  myelinated  dendrites, 
join  and  leave  the  capsule  of  the  organ  as  one  or  more 
fibres. 

These  organs  are  readily  visible  to  the  naked  eye,  measur- 
ing i  mm.  to  4  mm.  by  .1  mm.  to  .2  mm.  They  are  found 


94 


NKRVK    TISSl'KS. 


in  greater  numbers  in  the  small  muscles  of  the  hand  and 
foot. 

The  neurotendinous  beginnings  resemble  the  above  in 
structure,  with  the  exception  that  the  intrafusal  fibres  are 
tendon  bundles  and  the  amyelinated  fibres  do  not  wind 
around  the  intrafusal  fibres,  but  have  short  branches  that 
arise  in  little  plates  upon  the  tendon  bundles. 

The  Motor  endings  of  the  voluntary  muscles  are  chiefly 
from  myelinated  fibres.  After  piercing  the  epimysium,  the 


-    ;         ,. 


FIG.  34. — MOTOR  NERVE-ENDINGS  IN  INTERCOSTAL  MUSCLE  OF  A  RABBIT 

a.  Sensor  nerve  fibre;  b.  muscle  fibres;  c.  motor  plates;  d.  myelinated  nerve 

fibre;  e.  bundle  of  nerve  fibres  (Stohr's  Histology}. 

nerve  follows  the  septa  to  the  primary  bundles  and  breaks 
up  into  fibres  of  which  each  muscle  fibre  receives  one; 
no  doubt  one  nerve  fibre  supplies  many  muscle  fibres.  The 
neurilemma  and  myelin  sheath  of  the  nerve  fibres,  upon 
passing  through  the  sarcolemma  blend  with  it,  and  the  axis 
cylinder  breaks  into  fibrillae  each  of  which  forms  a  number 


MOTOR    ENDINGS.  95 

of  bulbous  enlargements  that  pass  to  a  sole-plate.  This 
sole-pla-te  consists  of  a  mass  of  nucleated,  granular  proto- 
plasm and  with  the  bulbous  nerve  masses  constitutes  the 
end- plate. 

The  cardiac  and  involuntary  nonstriated  muscles  are 
supplied  by  the  sympathetic  system.  These  nerve  fibres 
form  plexuses  of  delicate  fibres  at  the  intersections  of  which 
are  found  ganglia'  of  various  sizes.  Individual  branches 
extend  to  the  muscle  fibres,  but  the  exact  manner  of  ending 
is  not  understood. 


CHAPTER  VII. 


CIRCULATORY  SYSTEM. 

The  Circulatory  System  comprises  the  Heart,  Arteries, 
Capillaries,  Veins  and  the  circulating  fluid,  the  Blood. 

THE  HEART. 

The  Heart  is  the  most  important  member,  as  on  its  con- 
tractions depends  the  circulation.  It  is  a  thick  muscular 
organ  composed  of  three  coats,  the  ENDOCARDIUM,  MYOCAR- 
DIUM and  EPICARDIUM. 

The  ENDOCARDIUM  consists  of  a  lining  of  endothelial  cells 
which  rest  upon  the  subendothelial  (fibro-elastic)  tissue. 

The  endothelial  cells  are  flattened,  nucleated  plates  that 
have  an  irregular  outline  and  are  held  together  by  a  small 
amount  of  intercellular  cement.  They  differ  but  slightly 
from  those  found  within  the  vessels. 

The  sube'ndothelial  tissue  consists  of  a  network  of  white 
fibrous  and  yellow  elastic  tissues.  It  may  contain  a  few  in- 
voluntary nonstriated  muscle  fibres.  Here  also  are  seen 
some  partly  developed  heart  muscle  fibres,  called  Purkinje 
fibres;  the  fibrillae  are  few  and  form  a  peripheral  ring. 
They  are  common  in  some  mammalian  hearts,  and  in  man 
they  are  represented  by  the  terminals  of  the  Bundle  of  His. 

Guarding  the  auriculo- ventricular  orifices  and  the  open- 
ings into  the  pulmonary  artery  and  aorta  are  duplications 
of  the  endocardium  called  VALVES.  Around  the  openings  the 
fibro-elastic  tissue  is  condensed  to  form  a  ring-like  mass,  the 
ANNULI  FIBROSI.  These  rings  serve  as  origins  for  the  valves. 


HEART.  97 

The  VALVES  consist  of  two  layers  of  endotheliafr  cells,  con- 
tinuous at  the  edges,  separated  by  the  subendothelial  tissue 
in  which  the  inelastic  tissue  predominates.  The  auricular 
muscle  may  extend  for  a  short  distance  into  the  auriculo- 
ventricular  valves.  The  chorda  tendinea  consist  of  cords 
of  fibrous  tissue  surrounded  by  endothelial  cells.  Above 
they  are  attached  to  the  valves  and  below  to  the  papillary 
muscles.  The  SEMI  LUNAR  VALVES  possess  a  marginal  band 
with  a  central  enlargement,  the  corpus  Arantii.  Upon  each 
side  of  the  corpus  is  a  small  semilunar  fold  called  the 
lunula.  The  band  strengthens  while  the  corpus  and 
lunulae  ensure  complete  closure  of  the  valves. 

The  Atrioventricular  Bundle,  or  Bundle  of  His,  consists 
of  a  bundle  of  peculiar  fibres  that  connect  auricles  and 
ventricles.  It  arises  near  the  orifice  of  the  coronary  sinus, 
passing  forward  between  the  annulus  ovalis  and  the  auriculo- 
ventricular  septum  and  turns  down  into  the  auriculoven- 
tricular  septum  at  the  base  of  the  median  leaflet  of  the 
tricuspid  valve;  it  passes  into  the  pars  membranacea,  and  at 
the  beginning  of  the  muscular  portion  of  the  interventricu- 
lar  septum  it  divides  into  two  fasciculi,  one  for  each  ventricle. 
These  bundles  lie  just  beneath  the  endocardium,  surrounded 
and  insulated  by  fibrous  connective-tissue  sheaths.  Passing 
toward  the  apex  of  the  heart  each  bundle  upon  reaching 
the  lower  third  sends  branches  to  the  papillary  muscles  and 
there  forms  a  large  number  of  twigs  that  extend  in  all 
directions  over  the  ventricular  surface  and  come  into 
histologic  relation  with  the  cardiac  muscle  fibres. 

The  muscle  fibres  are  striated  but  the  sarcoplasm  pre- 
dominates. The  fibrillae  are  few  and  peripherally  placed, 
forming  a  circle  or  irregular  or  triangular  groups.  The  volume 
and  size  is  greater  than  in  the  ordinary  cardiac  fibres.  The 
pigmentation  is  localized  and  not  prominent.  The  cell- 
boundaries  cannot  be  definitely  located  so  that  these  cells 
7 


98  CIRCULATOKY    SYSTKM. 

form  a  syncytium.  These  fibres  represent  early  stages  of 
muscle  development  from  undifferentiated  protoplasm. 

The  MYOCARDIUM  consists  of  involuntary  striated  muscle. 
In  the  auricles  the  fibres  are  arranged  in  two  layers,  inner 
longitudinal  and  outer  circular.  In  the  ventricles  the  fibres 
cannot  be  separated  so  distinctly  into  layers.  Some  run 
longitudinally,  other  transversely,  while  the  greatest  num- 
ber have  an  oblique,  circular,  or  spiral  course,  forming  even 
a  figure  eight.  Owing  to  this  arrangement  distinct  lamellae 
cannot  be  formed.  Usually  incomplete  internal  and  ex- 
ternal longitudinal  layers  are  formed  between  which  are 
seen  the  circular  fibres  that  form  the  thickest  layer.  Be- 
sides the  latter  are  found  spiral  and  oblique  fibres  that  are 
present  chiefly  in  the  upper  and  lower  portions  of  the  left 
ventricle. 

TheEFiCARDiUM,  or  VISCERAL  LAYER  OF  THE  PERICARDIUM, 
consists  of  two  portions,  serous,  and  fibrous.  The  serous  part 
is  practically  a  duplication  of  the  endocardium  in  structure. 
It  consists  of  endothelial  cells  and  subendothelial  tissue.  It 
differs  from  the  endocardium,  however,  in  being  separated, 
usually,  from  the  myocardium  by  a  thin  layer  of  adipose 
tissue  and  in  possessing  no  muscle  fibres.  It  continues  up 
over  the  great  vessels  for  a  short  distance  and  is  then  re- 
flected over  a  thick  sac  of  fascia,  which  constitutes  the 
fibrous  portion.  This  part  is  continuous,  above,  with  the 
fascia  of  the  neck,  and  below  is  attached  to  the  diaphragm. 

The  blood-vessels  are  branches  of  the  coronary  arteries,  and 
their  relation  to  the  muscle  fibres  has  been  described  under 
Muscle  Tissues.  The  endocardium  is  nourished  by  the 
blood  that  flows  over  it. 

Lymphatics  are  present  in  all  the  coats  but  do  not  com- 
municate with  one  another  to  any  great  extent. 

The  nerves  are  from  both  systems.  Sympathetic  ganglia 
are  numerous. 


ARTERIES.  99 

• 

The  blood  is  sent  from  and  returned  to  the  heart  by  the 
Vessels.  Of  these  there  are  three  varieties,  i,  Arteries,  or 
Efferent  vessels;  2,  Capillaries,  or  Connecting  vessels;  3, 
Veins,  or  Afferent  vessels. 

i.  For  convenience  of  description,  the  Efferent  vessels 
(Arteries)  are  classed  as  LARGE,  MEDIUM  and  SMALL.  The 
LARGE  are  the  AORTA  and  PULMONARY  ARTERY;  the  MEDIUM 
the  remainder  of  the  named  arteries  of  the  body,  and  the 
SMALL,  the  unnamed  branches  that  gradually  become 
capillaries.  All  have  the  same  general  structure,  consisting 
of  three  coats,  TUNICAS  INTIMA,  MEDIA  and  ADVENTITIA; 
they  carry  the  blood  from  the  heart. 

As  the  medium-sized  artery  is  the  type,  its  description 
will  be  considered  first  and  then  the  differences  between  it 
and  the  others  will  be  pointed  out. 

MEDIUM-SIZED  ARTERY.  The  TUNICA  INTIMA,  or  INTERNA, 
consists  of  three  layers,  the  endothelial,  subendothelial  and 
an  internal  elastic  lamina. 

The  endothelial  cells  differ  but  little  from  those  lining  the 
heart.  They  rest  upon  the  subendothelial  fibro-elastic 
tissue.  Limiting  this  coat  externally  is  a  prominent  wavy 
band  of  elastic  tissue,  the  internal  elastic  lamina,  which 
does  not  take  the  ordinary  stain  well,  and  appears  as  a  light 
wavy  band. 

The  MEDIA  consists  chiefly  of  circularly  arranged  involun- 
tary nonstriated  muscle  tissue.  The  fibres  are  small  and 
closely  packed.  Elastic  fibres  in  moderate  quantities  are 
found  between  the  muscle  fibres  in  an  artery  of  this  size. 
Often  a  band  of  elastic  tissue  separates  this  layer  from  the 
adventitia.  This  is  the  external  elastic  lamina,  but  it  is 
neither  as  thick  nor  so  prominent  as  the  internal.  In 
some  vessels  (subclavian,  especially)  longitudinal  muscle 
fibres  are  seen  near  the  int>mY  .  .  ; 

The  ADVENTITIA,  or  EXTERNALS  a  thick  fibre-elastic  coat, 


IOO 


CIRCULATORY    SYSTEM. 


and  protects  the  vessel  from  undue  dilatation.  In  some 
vessels,  as  renal  and  splenic  arteries,  longitudinal  muscle 
fibres  are  found.  This  coat  contains  the  larger  trunks  that 


h- 


FIG.  35. — CROSS-SECTION  OF  A  MEDIUM-SIZED  ARTERY. 
a.   Intima;  b.  media;  c.  adventitia;  d.  endothelial  cells;   e.   subendothclial 
tissue;  /.  internal  elastic  lamina;  g.  circular  muscle  tissue;  h.  elastic 
fibres;  i.  external  elastic  lamina;  k.  white  fibrous  tissue;  /.  arteriole; 
m.  venule,  vasa  vasorum. 

nourish  the  vessels,  the  vasa  vasorum.     The  nervi  vasorum 
are    present  also,   and    form   branches    that    pass   to    the 
iriusclf '  coa't.  " 
'  lit  I.ARGE  ARTERIES  the  iNTiMA  is  not  so  distinct  and 


ARTERIES.  101 

gradually  fades  into  the  media.  The  inter  ml  elastic 
lamina  is  usually  not  present  as  such,  but  the  elastic  fibres 
have  fused  with  the  elastic  tissue  of  the  intima  to  form  the 
fenestrated  membrane  of  Henle.  The  media  is  not  very 
muscular,  as  it  contains  a  predominance  of  elastic  fibres 
that  give  it  an  elastic,  but  not  a  contractile,  character. 
The  same  is  true  of  the  large  branches  of  the  aorta  as  the 
iliacs,  innominate,- and  common  carotids.  The  adventitia 
differs  but  slightly. 

In  SMALL  ARTERIES,  the  intima  is  proportionately  thinner, 
and  the  elastic  lamina  quite  prominent  and  thick.  The 
media  is  proportionately  thicker  than  in  the  other  vessels. 
It  contains  very  little  elastic  tissue,  and^  no  jdastic 
lamina. 

As  the  vessels  become  reduced,  the  intima  is  the  first  to 
suffer;  the  subendothelial  tissue  disappears,  and  the  endo- 
thelial  cells  are  seen  to  rest  upon  the  elastic  lamina.  The 
media  becomes  attenuated  so  that  only  a  single  layer  of 
muscle  fibres  is  seen.  This  soon  becomes  reduced  to  a  few 
stray  fibres.  The  adventitia  becomes  greatly  reduced,  and 
is  represented  by  a  few  bundles  of  fibrous  tissue.  This  is 
practically  the  PRECAPILLARY  VESSEL.  It  is  succeeded  by 
the  Capillary. 

2.  The  Connecting  vessels  (Capillaries)  are  merely  delicate 
tubes  consisting  of  a  single  layer  of  endothelial  cells  placed 
end  to  end,  and  held  together  by  intercellular  cement.  The 
endothelium  is  held  by  some  to  be  phagocytic.  They  are  the 
smallest  vessels,  and  anastomose  freely  to  form  loose  or  dense 
plexuses.  The  loosest  mesh  is  found  in  muscles.  At  times 
they  are  very  irregular,  possessing  dilatations.  They  are 
practically  very  thin  animal  membranes,  and  through  their 
walls  the.  liquid  portion  of  the  blood  and  the  ameboid  white 
blood  cells  have  no  difficulty  in  passing  into  the  surrounding 
tissues.  Small  capillaries  average  5  to  7  microns  in  diame- 


102  CIRCULATORY    SYSTEM. 

ter,  and  cross-sections  show  that  they  are  encircled  by  two 
endothelial  cells.  Large  capillaries  average  8  to  13  mi- 
crons and  are  encircled  by  three  to  four  endothelial  cells. 
Stohr  claims  that  capillaries  can  contract  as  nerve  endings 
are  found  in  the  cells. 

In  muscles,  the  capillaries  run  parallel  to  the  course  of  the 
fibres,  and  are  connected  to  one  another  by  dilated  vessels, 
or  ampulla.  In  the  liver,  adrenal,  spleen  and  carotid 
gland,  the  endothelium  of  the  capillaries  is  usually  attached 
to  the  functionating  epithelium  or  parenchyma.  Such 
vessels  are  termed  sinusoids  (Minot).  In  the  kidney  are 
seen  little  arterial  capillary  tufts  interposed  between  two 
arterioles.  Such  structures  are  termed  rctia  mirabilui. 
In  the  penis,  the  arterioles  empty  into  cavernous  spaces,  or 
sinuses  without  forming  capillaries.  In  exposed  regions, 
nose,  ear,  toes,  kidneys  and  membranes  of  the  nervous 
system,  direct  connections  between  arteries  and  veins  exist. 
They  are  called  anastomoses. 

The  Afferent  vessels  (Veins)  have  the  same  general 
structure  as  arteries,  though  the  coats  are  all  thinner,  and 
collapse  more  readily;  they  carry  the  blood  toward  the 
heart. 

The  INTIMA  often  shows  no  internal  elastic  lamina;  when 
present,  it  is  not  prominent.  At  intervals,  this  coat  is 
thrown  into  folds  called  VALVES.  These  are  duplications 
of  the  intima,  and  are  usually  arranged  in  pairs.  At  the 
place  in  which  they  are  located,  the  vessels  are  usually 
slightly  dilated.  Valves  occur  in  all  the  veins  except  the 
portal,  pulmonary,  hepatic,  innominate,  common  iliacs, 
mesenteric,  splenic  and  renal  veins. 

The  MEDIA  contains  a  very  small  amount  of  muscle  tissue, 
but  is  reinforced  by  fibre-elastic  tissue.  In  some  veins,  the 
muscle  tissue  is  entirely  wanting  (brain  and  bones),  while 
in  others,  longitudinal  muscle  fibres  are  present  in  this  coat. 


VEINS.  103 

The  lack  of  muscle  tissue  accounts  for  the  collapsibility  of 
these  vessels. 

The  ADVENTITIA  is  the  most  prominent  coat,  and  may 
possess  longitudinal  muscle  fibres.  It  is  similar,  in  struc- 
ture, to  that  of  the  arteries. 

Blood-vessels  are  nourished   by  vessels   that  pierce   the 


d 

FIG.  36. — PORTION  OF  A  CROSS-SECTION  OF  A  HUMAN  VEIN. 

A.  Intima;  B.  Media;  C.  Adventitia — a.  internal  elastic  lamina;  b.  smooth 
muscle  fibres;  c.  white  fibrous  connective  tissue;  d.  smooth  muscle 
fibres  in  the  adventitia  (Stohr's  Histology}. 


adventitia  and  send  branches  to  the  media,  the  vasa 
vasorum.  The  intima  is  nourished  by  the  blood  that  flows 
over  it. 

The  NERVES  are  chiefly  sympathetic,  and  are  dis- 
tributed to  the  media  and  adventitia.  They  are  the  nervi 
vasorum. 

Vessels  are  often  the  centers  of  extensive  lymphatic  chan- 
nels that  lie  in  the  adventitia. 


104  CIRCULATORY   SYSTEM. 

Table  of  comparison  of  arteries  and  veins :— 


CHARACTER. 

ARTERIES. 

VEINS. 

Coats. 

Three. 

Three. 

Size. 

Thick. 

Thin. 

Intim. 

Elastic    lamina    promi- 

Not prominent;  may  be 

nent. 

absent. 

Media. 

Mainly  smooth  muscle. 

Little     muscle,     mainly 

white  fibrous  tissue. 

When  empty. 

Do  not  collapse  readily. 

Collapse  readily. 

Valves. 

Absent. 

Usually  present. 

Course   of    the 

blood. 

From  the  heart. 

Toward  the  heart. 

Character  of 

Oxygenated    (with     ex- 

Deoxygenated (with  ex- 

the blood. 

ception  of  that  in  the 

ception  of  that  in  the 

pulmonary  artery). 

pulmonary  veins). 

The  Blood  is  the  only  liquid  connective  tissue.  It  is  com- 
posed of  CELLULAR  ELEMENTS,  THE  CORPUSCLES,  and  the 
INTERCELLULAR  SUBSTANCE,  the  LIQUOR  SANGUINIS. 

The  CELLULAR  ELEMENTS  are  of  three  varieties,  the  RED 

CELLS,  WHITE  CELLS  and  PLATELETS. 

The  RED  CELLS,  or  ERYTHROCYTES,  are  non-nucleated, 
bell-shaped  elements  averaging  7  to  8.5  microns  in  diameter. 
The  bell-shape  is  not  seen  unless  the  necessary  precautions 
are  exercised,  that  is  to  fix  the  blood  before  it  becomes 
exposed  to  the  air  (see  Blood  Technic,  p.  27).  These  cells 
have  been  studied  under  various  conditions  by  Weiden- 
reich  and  Lewis  and  the  author  has  found  that  they  are  to  be 
readily  studied  in  fetal  tissues.  Upon  exposure  to  air  these 
bell-shaped  cells  collapse  and  this  accounts  for  the  usual 
description  as  that  of  a  biconcave  disc.  In  the  normal 
blood  these  cells  form  rouleaux  and  this  is  said  to  be  due  to 
the  cells  fitting  into  one  another.  When  exposed  to  air 
these  cells  collapse  and  resemble  rolls  of  coins  on  edge. 


RED    BLOOD    CELLS. 


105 


Under  the  microscope  each  cell  is  pale  straw-colored  or 
greenish.  It  consists  of  a  framework,  the  stroma,  that 
contains  an  inorganic  compound  that  carries  the  oxygen; 
this  is  the  hemoglobin.  The  presence  of  a  cell  membrane  is 
still  a  matter  of  dispute. 

Some  cells  average  from  5.5  to  7.5  microns,  and  are 
called  microcytes,  while  those  over  8.5  microns  are  macro- 


-, 


FIG  37. — BLOOD  CELLS. 

Red  blood  cells  i,  2,  3  and  4  i,  Bell-shaped  red  blood  cell  of  man; 
2,  surface  view  of  collapsed  bell-shaped  cell;  3,  side  view  of  2;  4,  surface 
view  of  red  blood  cell  of  the  frog. 

White  cells  5,  6  and  7.  5,  Small  lymphocyte;  6,  hyalin  cell;  7,  finely 
granular  oxyphil. 

cytes.  Bethe  found  the  various  red  cells  in  the  following 
proportions:  6.92  microns,  42  per  cent.;  7.26  microns,  28 
per  cent. ;  8.58  microns,  16  per  cent. ;  6.6  microns,  8  per  cent. ; 
9.24  microns,  6  per  cent. 

In  normal  blood,  the  cells  tend  to  form  rolls,  or  rouleaux. 
Under  the  same  condition,  5,000,000  corpuscles  are  found, 


106  CIRCULATORY    SYSTEM. 

per  cubic  mm.,  in  the  male,  and  about  4,500,000  in  the 
female. 

Nucleated  red  cells,  or  erythroblasts,  are  found  in  the  fetus, 
in  bone-marrow  and  the  spleen.  The  cell  of  average  size  is 
called  a  normoblast,  the  smaller,  a  microblast,  and  the 
larger,  a  macroblast.  In  fishes,  reptiles,  birds  and  amphib- 
ians, the  red  cells  are  nucleated.  In  all  mammals,  they  are 
circular,  except  in  the  camel  family,  in  which  they  are  oval. 
In  the  frog,  the  red  cells  are  very  large,  oval,  biconcave, 
nucleated  discs  that  are  far  larger  than  the  same  cells  in  man. 

The  size  of  the  red  cell  is  by  no  means  proportionate  to 
that  of  the  animal.  The  musk  deer  possesses  one  of  the 
smallest  (2.4  microns),  while  the  proteus  has  about  the 
largest  (62.5  microns).  That  of  the  elephant  is  but  9.2 
microns  in  diameter,  and  beside  it  stands  that  of  the  hum- 
ming bird,  with  a  diameter  of  nearly  9.4  microns. 

The  red  cells  are  more  numerous  in  carnivorous  than  in 
herbivorous  animals,  while  in  birds  they  are  larger  in  size. 
In  the  amphibians,  where  the  size  is  great,  the  number  is 
small. 

According  to  Malassez  and  Hayem,  each  cu.  mm.  of 
goat's  blood  contains  18  to  19  millions  of  red  cells;  birds  2 
to  3  millions;  reptiles  0.5  to  1.6  millions;  frogs  400,000; 
proteus  36,000;  bony  fishes  i  to  2  millions;  torpedo  140,000. 

WHITE  BLOOD  CELLS,  or  LEUKOCYTES,  are  large,  pale  cells 
readily  distinguished  from  the  above.  About  5,000  to 
8,000  are  found  in  each  cubic  mm.  of  blood,  and  some  of  the 
varieties  have  the  powers  of  motion  and  phagocytosis. 

They  are  classified  as  follows: 

1.  LYMPHOCYTES  (SMALL  LYMPHOCYTES). 

2.  HYALIN  CELLS  (LARGE  LYMPHOCYTES). 

3.  POLYMORPHONUCLEAR  LEUKOCYTES,  Or  FINELY  GRANU- 
LAR OXYPHILS  (Formerly  neutrophil). 


WHITE    BLOOD    CELLS.  107 

4.  COARSELY  GRANULAR  OXYPHILS  (Formerly  acidophil). 

5.  FINELY  GRANULAR  BASOPHILS. 

6.  COARSELY  GRANULAR  BASOPHILS. 

1.  The  LYMPHOCYTES  average  5   to   11   microns.     Each 
consists  of  a  large  darkly  staining  nucleus  surrounded  by  a 
narrow   rim   of    faintly   stained   protoplasm.      It   is   both 
ameboid  and  phagocytic,  and  constitutes  about  15  to  30 
per  cent,  of  all  the  white  cells. 

2.  The  HYALIN  CELL  averages  11   to  15  microns.     Both 
nucleus    and    protoplasm    stain    but    faintly,    hence    the 
name.     In    the  protoplasm  some    basophilic  granules  are 
occasionally  seen.     It  is  actively  ameboid  and  phagocytic. 
It  represents  2  to  6  per  cent,  of  the  white  cells. 

3.  POLYMORPHONUCLEAR  LEUKOCYTES,  Or  FINELY  GRANU- 
LAR    OXYPHILS,    F.     G.    ACIDOPHILS,    Or     F.    G.     EOSINOPHILS, 

average  7.5  to  n  microns.  The  nucleus  has  many  shapes, 
as  U,  V,  W,  etc.,  and  may  even  be  divided  in  a  number  of 
segments  (polynuclear) .  The  protoplasm  contains  a  num- 
ber of  fine  granules  that  take  the  acid  stain  deeply.  These 
granules  were  at  one  time  regarded  as  neutrophilic,  and  the 
cells  were  called  neutrophils.  They  are  actively  ameboid  and 
phagocytic,  and  represent  60  to  72  per  cent,  of  all  leukocytes. 

4.  The  COARSELY     GRANULAR    OXYPHIL,    C.    G.    ACIDOPHIL, 

or  EOSINOPHIL,  is  about  7  to  10  microns  in  diameter.  The 
protoplasm  contains  a  few  large  granules  that  take  the  acid 
stain  deeply.  It  was  formerly  called  acidophil,  or  eosino- 
phil,  and  is  actively  ameboid,  but  not  phagocytic.  It  repre- 
sents .1  to  4  per  cent,  of  the  leukocytes,  though  rarely 
over  2  per  cent,  except  in  childhood. 

5.  The  FINELY  GRANULAR  BASOPHiL  resembles  GROUP  3, 
except  that  the  granules  take  a  basic  stain,  and  are  present 
to  the  extent  of  .1  to  i  per  cent.,  but  usually  under  .25  per 
cent. 


108  CIRCULATORY    SYSTEM. 

6.  The  COARSELY  GRANULAR  BASOPHiL  is  said  to  be 
absent  from  normal  blood.  It  is  a  relatively  large  cell,  and 
is  also  called  the  mast  cell. 

Another  cell  that  is  usually  described  among  the  leuko- 
cytes is  the  myelocyte,  or  marrow  cell.  This  cell  is  not  a 
normal  constituent  of  the  blood,  but  is  found  there  in  certain 
blood  diseases.  (See  Bone-marrow,  p.  73.) 

The  BLOOD  PLATELETS,  or  THROMBOCYTES,  are  small  (2  to  4 
microns),  oval  or  circular  discs,  capable  of  ameboid  move- 
ment. They  number  about  200,000  to  300,000  per  cubic 
mm.  Their  function  and  origin  are  unknown.  They 
can  readily  be  found  in  blood  fixed  in  a  i  per  cent,  osmic 
acid  solution. 

In  certain  diseases  the  platelets  are  increased  while  in 
others  they  are  diminished. 

According  to  Helber,  platelets  are  not  found  in  the  blood 
of  frogs  or  birds. 

The    INTERCELLULAR   SUBSTANCE,    Or    LIQUOR    SANGUINIS, 

contains  the  salts  of  the  blood.  Its  density  is  such  that  the 
cells  retain  their  normal  shape.  If,  however,  solutions  are 
added  that  differ  in  density,  the  action  upon  the  cells  is 
characteristic. 

Upon  the  addition  of  strong  salt  solution,  the  cells  become 
irregular  in  outline,  and  are  crenated.  If  water  be  added,  it 
dissolves  the  hemoglobin,  and  the  cells  swell  and  become 
spherical,  but,  as  a  rule,  are  not  destroyed. 

The  action  of  acetic  acid  is  important.  The  addition  of  a 
.3  per  cent,  solution  decolorizes  the  red  cells  and  renders  the1 
white  cells  more  distinct.  This  is  made  use  of  in  Hema- 
tology  for  the  purpose  of  counting  the  white  cells,  in  a  fresh 
condition. 

When  blood  clots,  fibrin  is  precipitated,  and  this  entangles 
the  corpuscles. 

HEMOGLOBIN  is  an  organic  compound  of  iron,  and,  as  it 


HEMAL    GLANDS. 


I 


I09 


exists  in  the  blood,  it  cannot  be  readily  studied.  Its  con- 
version into  the  crystalline  state  is  not  difficult. 

HEMOGLOBIN  CRYSTALS  will  be  formed  if  a  drop  of  de- 
fibrinated  blood  be  mixed  with  a  drop  of  Canada  balsam,  or 
clove  oil,  and  covered  with  a  cover-glass.  They  are  large, 
red,  tetrahedral  crystals. 

HEMIN  CRYSTALS  may  be  prepared  by  adding  a  small 
crystal  of  salt  arid  two  drops  of  glacial  acetic  acid  to  a  little 
dried  blood,  and  heating  until  the  mixture  boils.  During 
this  process  it  should  be  covered.  When  cool,  small 


FIG.  38. 

i.  Hemin  crystals  of  man  (  X56o);  2.  crystals  of 
common  salt;  3.  hematoid  crystals  of  man 
(Stohr's  Histology}. 


FIG.  39. — HEMOGLO- 
BIN CRYSTALS  OF  A 
DOG  (Xioo);  a 
crystal  separating 
into  fibres  (Stohr's 
Histology). 


brownish  crystals  will  be  found.  These  may  be  single  or 
grouped  in  the  form  of  rosettes,  and  are  known  as  Teich- 
mann's  crystals. 

Among  the  blood-making  organs  are  placed  the  COCCY- 

GEAL  and  CAROTID  GLANDS. 

The  former,  LUSCHKA'S  GLAND,  is  found  in  front  of  the 
coccyx,  and  is  joined  to  the  middle  sacral  artery.  It  is 
surrounded  by  a  fibrous  sheath,  which  sends  in  septa  that 
divide  the  organ  irregularly  into  areas,  or  compartments. 
The  latter  contain  groups  of  polyhedral  cells  surrounded  by 
dense  plexuses  of  capillaries.  Nonmyelinated  nerve  fibres 
are  numerous. 


HO  CIRCULATORY    SYSTKM. 

The  CAROTID  GLAND  is  found  at  the  bifurcation  of  the  com- 
mon carotid  artery,  and  its  structure  is  the  same  as  that  of 
Luschka's  gland. 

HEMOLYMPH  NODES. — These  organs  vary  in  size  from  a 
pin  head  to  a  large  bean  and  are  found  in  abundance  in  the  re- 
troperitoneal  and  cervical  regions  and  less  numerous  else- 
where. Each  is  surrounded  by  a  capsule  of  white  fibrous  and 
yellow  elastic  tissues,  containing  a  little  smooth  muscle 
tissue;  trabeculae  pass  in  and  form  the  framework  of  the 
organ.  In  the  framework  are  found  red  and  white  blood- 
cells.  Of  the  latter,  the  lymphocytes  are  the  most  numer- 
ous; besides  these  hyalin,  finely  granular  oxyphils  and 
basophils  are  found  in  varying  numbers.  In  addition, 
mononuclear  phagocytes  that  contain  pigment  and  disinte- 
grating red  cells  are  seen.  Beneath  the  capsule  and 
following  the  trabeculae  to  the  hilus  are  seen  sinuses  that 
do  not  contain  lymph  but  blood. 

These  organs  usually  possess  no  lymphatics.  The  blood- 
vessels enter  at  the  hilus  and  form  capillaries  within  the 
organ;  these  capillaries  communicate  with  the  blood 
sinuses.  The  larger  views  are  in  the  trabeculae  and  end  in 
thin-walled  lacunae  that  possess  perforated  walls,  by  means 
of  which  they  communicate  with  the  blood  sinuses. 

Certain  atypic  organs  possess  lymphatics.  Nerves  are 
present  and  probably  pass  to  the  smooth  muscle  tissue. 

Some  of  these  structures  resemble  the  spleen  in  structure, 
others  the  marrow  and  still  others  ordinary  lymph  nodes. 

Parasympathetics,  or  Aortic  Bodies. — These  are  two  to 
four  brownish  bodies  found  in  the  neighborhood  of  the 
inferior  mesenteric  artery  and  closely  related  with  the  aortic 
sympathetic  plexus.  Each  is  surrounded  by  a  capsule  of 
white  fibrous  connective  tissue  that  sends  in  trabeculae 
that  form  the  framework  of  the  organ.  In  the  meshes  of 
this  framework  are  found  the  epithelium  which  consists  of 


BLOOD    VESSELS    AND    NERVES.  Ill 

groups  of  polygonal  or  cuboidal  cells  closely  packed  and 
of  the  chromaffin  type. 

The  blood-vessels  derived  from  the  aorta,  or  inferior 
mesenteric  artery,  follow  the  trabeculae  and  form  a  rich 
capillary  plexus  around  the  epithelial  cell-groups. 

The  nerves  are  from  the  sympathetics  and  their  relation 
and  arrangement  is  similar  to  the  nerves  of  medulla  of  the 
adrenal.  These  organs  are  found  chiefly  in  childhood. 


CHAPTER  VIII. 


THE  LYMPHATIC  SYSTEM. 

The  Lymphatic  System  includes  the  Lymphatic  and 
Thoracic  Ducts,  capillaries  and  intermediate  vessels,  and  a 
number  of  organs,  Lymph  Node  (Lymphatic  Gland),  Spleen 
and  Thymus  Body. 

The  ducts  resemble  veins  more  than  arteries.  Their 
walls  are  thin,  and  they  possess  valves.  The  arrangement 
of  the  muscle,  and  the  distribution  of  the  nerves,  are  like 
those  of  an  artery. 

Lymph  capillaries  are  much  larger  than  those  of  the 
vascular  system,  measuring  30  to  60  microns  in  diameter. 

Lymphoid    tissue  is    arranged    in   four  ways,    DIFFUSE, 

SOLITARY    FOLLICLES,     AGMINATED     FOLLICLES     AND    LYMPH 

NODES,  or  LYMPHATIC  GLANDS.  The  first  three  have  been 
considered  under  Lymphoid  Tissue.  (See  Connective  Tis- 
sues, p.  66). 

Lymph  Nodes,  or  Glands,  are  small,  bean-shaped  organs, 
surrounded  by  a  CAPSULE,  and  composed  of  CORTEX,  ME- 
DULLA and  HILUS. 

The  CAPSULE  consists  of  white  fibrous  tissue  and  contains 
some  yellow  elastic  and  smooth  muscle  tissues;  beneath  is 
a  lymph  space  or  sinus.  From  the  inner  surface  of  the 
capsule,  trabeculcB  are  sent  into  the  cortex,  and  these 
divide  the  latter  into  a  number  of  masses  called  secondary 
follicles,  or  nodules.  The  lymph  space  continues  along  the 
trabeculae. 

The  CORTEX  contains  the  secondary  nodules  and  tra- 
beculcz.  The  former  consist  of  dense  lymphoid  tissue,  and 

112 


LYMPH    NODE.  113 

contain  a  germinal  center.  The  cells  are  chie'fiy  lympho- 
cytes, which  are  arranged  in  concentric  layers  around  the 
periphery.  Other  cells  of  the  hyalin  variety  are  found  in 
the  central  portion.  During  gestation,  nucleated  red  cells 
may  be  present.  The  follicles  continue  into  the  center  of 
the  node  as  the  medullary  cords. 


FIG.  40. — LONGITUDINAL  SECTION  OF  A  LYMPH  NODE. 

a.  Hilus;  b.  arteriole;  c.  venous  sinuses;  d.  adipose  tissue;  e.  secondary  nodule 
of  cortex;  /.  vein  in  medulla;  g.  subcapsular  lymph  sinus;  h.  germinal 
center  of  secondary  nodule;  i,  i.  trabeculae;  k.  capsule;  /.  lymph  sinus; 
m.  medullary  cord. 

The  trabecula  separate  the  follicles  from  one  another, 
and  pass  into  the  medulla  surrounded  by  the  lymph  space. 

The  MEDULLA  consists  of  the  medullary  cords  and 
trabeculce. 

The  cords  are  the  band-like  continuations  of  the  second- 
ary follicles,  and  are  separated  from  the  trabeculae  by  the 
lymph  spaces  that  accompany  the  latter.  They  consist  of 
dense  lymphoid  .tissue,  supported  by  reticulum.  At  the 
hilus,  the  medulla  comes  to  the  surface. 


114  THE    LYMPHATIC    SYSTEM. 

The  HILUS  is  a  scar-like  depression  at  one  side,  where 
the  vessels  enter  and  leave.  At  this  place,  the  secondary 
nodules  are  wanting,  and  the  medulla  comes  to  the  surface. 

The  arterial  vessels,  to  a  great  extent,  enter  at  the  per- 
iphery of  the  node.  Their  branches  continue  into  the 
trabeculae,  and  then  pass  into  the  follicles.  Those  that 
enter  at  the  hilus  also  follow  the  trabeculae,  and  bridge  the 
sinuses  to  enter  the  lymphoid  tissue. 

The  venous  radicals  all  pass  toward  the  hilus,  where  one 
or  more  vessels  may  be  formed  that  carry  all  the  blood 
away. 

The  afferent  lymph  vessels  pierce  the  capsule  at  different 
points,  and  empty  into  the  capsular  sinus.  The  lymph 
passes  down  along  the  trabeculae,  and  niters  through  the 
organ.  All  the  lymph  is  collected  into  one  or  more  efferent 
vessels  that  leave  at  the  hilus. 

Lymph  nodes  are  the  highest  form  of  lymphoid  tissue. 
They  are  scattered  throughout  the  lymphatic  system,  in 
the  pathways  of  the  vessels.  They  are  often  collected  into 
groups,  as  in  the  axillary,  inguinal  and  femoral  regions. 

Lymph  nodes  are  uncertain  structures,  as  they  may 
disappear  early,  or  change  from  place  to  place.  They  make 
the  white  blood-cells,  filter  the  lymph,  are  the  centers  of  cell 
destruction,  and  may  possibly  give  rise  to  red  blood-cells, 
as  in  the  female  during  pregnancy. 

SPLEEN. 

The  Spleen  is  a  lymphoid  structure,  surrounded  by  a 
capsule  of  dense  white  fibrous  tissue  that  contains  invol- 
untary non-striated  muscle  fibres,  and  limits  the  splenic 
substance. 

The  capsule  sends  in  trabeculce  that  divide  the  organ  ir- 
regularly into  compartments.  At  one  side  is  a  depression, 
the  HILUS,  at  which  the  vessels  enter  and  leave. 


SPLEEN.  115 

The  splenic  substance  consists  of  two  main  portions,  the 

PULP  and  MALPIGHIAN  Or  SPLENIC  CORPUSCLES. 

The  PULP  is  composed  of  diffuse  lymphoid  tissue,  dis- 
integrating red  cells,  nucleated  red  cells  and  some  large 
polynuclear  elements.  To  the  red  cells  the  peculiar  color  is 
due,  and  the  organ  has  been  called  the  "  grave-yard  of  the 
red  cells."  The  cells  are  supported  by  retiform  connective 
tissue. 


FIG.  41. — SECTION  OF  SPLEEN. 

fl.  Capsule;  b.  trabeculae,  longitudinal  section;  c.  pulp;  d.  splenic  corpuscle; 
e.  germinal  center  of  corpuscle;  /.  eccentric  arteriole  in  corpuscle;  g. 
trabecula,  cross-section;  h.  blood-vessel. 

The  SPLENIC  CORPUSCLES  are  solitary  follicles  and  consist 
of  dense  lymphoid  tissue.  They  differ  from  the  ordinary 
follicle  in  possessing  an  eccentric  ally- placed  arteriole.  This 
lymphoid  tissue  is  held  to  be  in  the  adventitial  sheath  of 
the  arteriole,  and  forms  a  spherical  mass  at  the  bifurcation 
of  the  vessel.  These  follicles  usually  show  germinal  centers. 


Il6  THE    LYMPHATIC    SYSTEM. 

The  circulatory  system  of  the  spleen  is  peculiar  in  being 
an  open  one.  Capillaries,  as  such,  do  not  exist,  and  the 
arterioles  and  venules  are  connected  by  blood  spaces,  or 
ampulla. 

The  splenic  artery  enters  at  the  hilus,  and  breaks  into 
branches  that  follow  the  trabeculae.  Of  these,  some 
quickly  pass  into  the  pulp,  while  others  follow  the  tra- 
beculae to  their  smallest  divisions.  The  spleen  is  divided  into 
lobules,  about  one  mm.  in  diameter,  each  one  of  which  is 
further  subdivided  into  histologic  units,  one  for  each  termi- 
nal artery,  or  ampulla.  These  terminal  vessels  are  covered 
by  a  lymphatic  sheath,  the  ellipsoidal  sheaths.  The 
terminal  ampullae  are  porous,  and  continue  as  veins. 

The  spleen  is  subject  to  rhythmic  contractions,  one  per 
minute,  and  about  18  per  cent,  of  its  volume  is  lost  at  each 
contraction.  These  are  produced  by  the  involuntary 
muscle  in  the  capsule  and  trabeculae.  When  the  cardiac 
impulse  sends  the  blood  into  the  arteries,  the  blood  passes 
into  the  ampullae,  and  through  the  porous  walls  into  the 
pulp.  When  the  rhythmic  contractions  occur,  the  blood  is 
forced  into  the  veins,  and,  at  the  same  time,  the  arteries  are 
closed.  This  shows  an  open  circulation  (Mall). 

Lymphatics  occur  in  the  capsule  and  trabeculae  only. 

THYMUS  BODY. 

The  Thymus  Body  is  essentially  a  lymphoid  structure, 
though  it  undergoes  peculiar  changes  in  its  life  history. 

It -originates  as  a  true  gland  (epithelial  organ),  but  soon 
leukocytes  infiltrate  it,  and  cause  the  disappearance  of  the 
epithelium,  except  small  islands.  After  the  sixth  year,  it 
generally  undergoes  further  change.  The  lymphoid  tissue 
is  gradually  replaced  by  adipose  tissue,  so  that  an  old  thy m us 
will  show  but  little  lymphoid  tissue. 

This  organ  is  surrounded  by  a  capsule  of  white  fibrous 


THYMUS    BODY.  1 17 

tissue  that  sends  in  septa,  which  divides  the.organ  into 
LOBES  and  LOBULES. 

Each  LOBULE  consists  of  cortex  and  medulla. 

The  CORTEX  is  composed  of  dense  lymphoid  tissue,  and 
stains  deeply,  owing  to  the  large  number  of  leukocytes 
present.  The  MEDULLA  consists  of  diffuse  lymphoid  tissue, 
and  takes,  therefore,  a  lighter  stain.  The  supportive  tissue 
is  reticulum. 


FIG.  42. — SECTION  OF  THE  THYMUS  BODY  OF  A  CHILD. 
a.  Capsule;  b.  interlobular  connective  tissue;  c,  c.  adipose  tissue;  d.  blood- 
vessels in  interlobular  tissue;  e.  cortex;  /.  mzdulla;  g.  blood-vessel  in 
lobule;  h,  h.  corpuscle  of  Hassal;  i.  corpuscle  of  Hassal  magnified. 

In  the  medulla,  are  found  small,  peculiar  bodies,  con- 
sisting of  concentrically  arranged  epithelial  cells;  these  are 
the  thymic  corpuscles,  or  corpuscles  of  Hassal.  They  are  sup- 
posed to  represent  the  remains  of  the  epithelium,  though 
some  hold  that  they  represent  endothelium  of  blood-vessels. 
These  bodies  are  encapsulated,  and  may  be  compound. 

The  blood-vessels  pierce  the  capsule,  and  form  branches 
in  the  interlobular  connective  tissue.  From  these,  capil- 
laries enter  the  lobules  and  are  distributed  to  the  lymphoid 
tissue. 


CHAPTER  IX. 


ALIMENTARY  TRACT. 

The  Alimentary  Tract  starts  at  the  lips,  and  extends  to 
the  anus.  It  receives  the  food,  digests  it  and  casts  off  that 
which  is  undigested.  The  various  portions  perform  differ- 
ent functions,  and  the  lining  cells  differ  accordingly.  The 
inner  coat  is  a  mucous  membrane  that  gives  rise  to  glands, 
which  are  devices  of  nature  for  increasing  the  secretory 
surface.  The  absorptive  surface  is  increased  by  prolon- 
gations of  the  mucosa  into  the  lumen  of  the  organ  (villi  of 
the  small  intestine). 

The  Lip  is  covered  externally  by  SKIN,  and  internally  by 
MUCOUS  MEMBRANE.  Between  these,  are  found  connective 
tissue  and  muscle. 

The  SKIN  consists  of  two  portions,  the  epithelial,  or 
epidermis,  and  the  connective  tissue  portion,  or  derma. 

The  epidermis  is  composed  of  stratified  squamous  cells, 
of  which  two  layers,  the  stratum  corneum  and  stratum  Mal- 
pighii  are  distinct.  The  stratum  corneum  is  the  outer,  and 
consists  of  nonnucleated  scales;  the  stratum  Malpighii  is 
the  genetic  portion.  Its  lowest  cells  rest  upon  a  basement 
membrane,  and  are  columnar  in  shape.  Those  above  are 
polyhedral;  the  latter  become  more  flattened  as  the  corneum 
is  approached.  The  derma  consists  of  white  fibrous  con- 
nective tissue  supporting  blood-vessels,  nerves  and  lym- 
phatics. Beneath  the  epithelium  it  is  thrown  into  waves 
called  papillce. 

The  mucous  surface  is  also  lined  by  stratified  squamous 
cells,  that  differ  from  the  outer,  however,  in  being  larger 

118 


TKKTII.  119 

and  less  readily  stained.  The  cells  rest  upon  a  basement 
membrane,  beneath  which  is  the  tunica  propria,  composed  of 
papillated,  delicate  fibro-elastic  tissue. 

Between  the  tunica  propria  and  skin,  are  found  connec- 
tive tissue  and  voluntary  striated  muscle.  Near  the  tunica 
propria  are  to  be  seen  small,  compound  tubular  glands  that 
open  upon  the  mucous  surface.  At  the  margin  of  the  lip 
these  two  surfaces  join,  and  this  is  the  muco-cutaneous 
junction;  here  the  epithelial  layer  is  quite  thick,  and  the 
cells  are  larger  and  bladder-like,  resembling  the  epitrichial 
cells  of  the  fetus. 

Blood-vessels  are  found  in  great  abundance,  and  form 
dense  plexuses,  especially  around  the  glands. 

The  Mouth  is'lined  by  a  MUCOUS  MEMBRANE,  consisting 
of  stratified  squamous  cells  resting  upon  a  basement  mem- 
brane and  tunica  propria.  Here  and  there  are  found  small 
glands  of  the  same  nature  as  those  found  in  the  lips. 

THE  TEETH. 

The  Teeth  are  the  chief  organs  of  mastication  and  are 
adapted  for  cutting,  grinding,  holding,  etc.  Each  consists, 
anatomically,  of  CROWN,  that  portion  above  the  gum; 
ROOT  or  FANG,  that  portion  in  the  jaw;  NECK,  the  narrow 
portion  between  the  preceding,  covered  by  the  gum. 

Histologically  considered,  there  is  the  ENAMEL  that 
covers  the  crown;  the  DENTIN  that  forms  the  bulk  and  gives 
the  shape  of  the  tooth;  the  CEMENTUM  that  covers  the  den  tin 
of  the  fang;  the  PERIDENTAL  MEMBRANE  that  surrounds  the 
root  and  holds  the  tooth  in  place;  the  PULP  that  occupies 
the  pulp  cavity  and  is  the  nutritive  and  sensitive  portion 
of  the  organ.  In  the  root  of  the  tooth  is  a  canal  that  leads 
into  the  PULP  CHAMBER;  this  is  the  ROOT  CANAL. 

The  enamel  is  the  hardest  substance  in  the  body  and 


120  ALIMENTARY   TRACT. 

forms  a  cap-like  covering,  of  varying  thickness,  of  the 
dentin.  It  is  thickest  at  the  cutting  or  occlusal  surface 
of  the  teeth  and  diminishes  in  thickness  as  the  root  is  ap- 
proached. It  is  said  to  consist  of  97  per  cent.,  or  more,  of 
inorganic  matter  and  3  per  cent.,  or  less,  of  organic  matter. 

The  enamel  consists  of  hexagonal  enamel  prisms  that 
are  arranged  perpendicular  to  the  surface  of  the  dentin, 
and  represent  modified  epithelial  cells.  Each  ENAMEL 
PRISM  or  FIBRE  has  a  wavy  or  tortuous  course  with  its 
inner  end  fitting  into  a  slight  depression  in  the  dentin. 
The  prism  is  of  the  same  diameter  throughout,  though  the 
sides  may  not  be  straight  and  even.  As  a  result,  near  the 
surface  of  the  tooth  shorter  additional  prisms  are  found 
and  these  are  the  SUPPLEMENTAL  PRISMS.  The  prisms 
seem  to  be  held  together  by  a  transparent  cement  which  is 
apparently  inorganic  in  composition.  In  a  prepared 
section  of  the  tooth  are  seen  some  brown  striations  that 
run  almost  parallel  to  the  surface  of  enamel  or  dentin  and 
in  the  latter  instance  may  run  the  entire  extent  of  the 
crown.  These  are  the  "brown  striae  of  Retzius. "  The 
cause  of  these  striae  is  still  in  dispute.  Tomes  believes  that 
they  represent  successive  positions  of  the  enamel  cap. 

When  studied  with  reflected  light  the  "lines  of  Schreger" 
are  seen  in  the  enamel.  These  are  apparently  due  to 
various  directions  taken  by  the  different  bundles  of  enamel 
prisms,  and  are  well  marked  near  the  surface  of  the  dentin 
and  less  so  toward  the  surface  of  the  enamel. 

Dentin.— This  portion  forms  the  bulk  of  the  tooth  and 
gives  it  its  shape.  It  is  yellowish-white  in  color,  harder 
than  bone,  and  represents  ivory.  It  is  everywhere  covered 
by  either  enamel  or  cementum.  It  is  composed  of  about 
72  per  cent,  of  inorganic  matter  and  of  about  28  per  cent, 
of  organic  matter. 

The  parts  of  importance   are   the  DENTINAL  SHEATHS, 


TEETH. 


121 


MATRIX,    and    DENTINAL   FIBRES.       The    DENTINAL   SHEATHS, 

or  NEUMANN'S  SHEATHS,  are  delicate  tube-like  masses  of 


4  -. 


FIG.  43. — LONGITUDINAL  SECTION  OF  AN  INCISOR  TOOTH 

A.  Crown;  B.  Neck;  C.  Fang;  i.  enamel;  2.  dentin;  3.  pulp-cavity;  4.  ce- 

mentum;  5.  root-canal  (after  Stohr's  Histology}. 

dense  dentin  that  seem  indestructible  and  will  persist  when 
the  matrix  has  been  destroyed.     They  extend  in  a  curved 


122  ALIMENTARY    TRACT. 

or  spiral  course  from  the  pulp  cavity  to  the  enamel  or 
cementum,  diminishing  in  diameter  as  they  pass  outward. 
Within  the  sheaths  are  spaces  called  DENTINAL  TUBULES  or 
CANALICULI.  They  radiate  from  the  pulp  cavity  to  the 
periphery  and  have  the  same  curved  or  spiral  course  of  the 
sheaths.  They  diminish  in  diameter  from  within  outward, 
and  terminate  at  the  enamel  or  cemental  surface  either 
by  anastomosing  with  one  another,  ending  bluntly  or 
opening  into  the  interglobular  spaces.  The  pulp  cavity 
end  is  usually  funnel-shaped  and  the  tubules  here  are 
closely  packed  so  that  there  is  very  little  matrix.  The 
tubules  branch  toward  the  enamel  or  cementum.  The 
curvatures  of  the  tubules  are  long  and  short,  or  primary 
and  secondary,  respectively. 

The  DENTINAL  FIBERS,  or  TOME'S  FIBRES,  represent  the 
processes  of  the  odontoblasts  and  they  occupy  the  dental 
tubules,  branching  as  the  latter  do  and  diminishing  in 
size  as  the  tubules  become  smaller.  Some  claim  that  they 
do  not  belong  to  the  odontoblasts,  but  represent  nerve 
tissue  surrounded  by  connective  tissue. 

The  MATRIX  occupies  the  space  between  the  dentinal 
sheaths.  It  consists  of  a  more  or  less  homogeneous  dentin 
that  is  not  so  hard  as  that  surrounding  the  canaliculi  in 
the  form  of  the  dentinal  sheaths.  It  is  less  abundant 
near  the  pulp  cavity,  as  the  sheaths  here  are  very  close 
together.  Farther  out,  as  the  sheaths  become  smaller  in 
diameter,  the  matrix  increases  along  the  margin  of  the 
dentin  near  the  enamel,  a  varying  number  of  small  irregu- 
lar spaces,  the  interglobular  spaces,  are  seen;  these  repre- 
sent areas  of  imperfect  calcification  and  they  are  filled  with  a 
gelatinous  substance.  Between  dentin  and  cementum 
these  spaces  are  smaller,  and  under  low  power  give  a 
granular  appearance  to  the  area;  this  represents  "  Tome's 
granular  layer." 


TEETH.  123 

Cementum. — This  is  a  bone-like  substance  tfyat  covers  the 
root  of  the  tooth.  It  consists  of  about  66  per  cent,  inor- 
ganic matter  and  34  per  cent,  organic  matter.  It  is 
thickest  at  the  apex  of  the  tooth  and  becomes  gradually 
thinner  as  the  cervix  or  neck  is  approached  and  ends 
at  the  lower  margin  of  the  enamel.  It  resembles  bone  very 
closely,  contains  LACUNA  CANALICULI  and  LAMELLA,  but 
no  Haversian  systems.  The  LAMELLA  are  about  the  same 
in  number  but  thicker  at  the  apex  than  near  the  cervix. 
This  applies  to  young  teeth.  In  older  teeth  the  layers  are 
not  only  much  thicker  near  the  apex  but  are  also  more 
numerous,  the  shorter  added  lamellae  constituting  sup- 
plemental lamella.  The  layers  may  or  may  not  run  parallel 
to  the  den  tin.  Passing  through  the  lamellae  at  varying  inter- 
vals are  fibres  that  seem  to  bind  the  layers  together,  resem- 
bling the  fibres  of  Sharpey.  Between  the  lamellae  are  irregu- 
lar spider-like  spaces  that  resemble,  but  vary  in  size,  shape 
and  number  of  canaliculi,  those  of  bone;  they  lie  partially  in 
one  layer  and  partially  in  another  and  their  long  axes  are 
parallel  to  the  surface  of  the  tooth.  Extending  out  from 
the  lacunae  are  the  CANALICULI  which  usually  are  directed 
peripherally,  though  some  are  seen  extending  in  all 
directions. 

The  CEMENTOBLASTS  occupy  the  lacunae.  They  are  oval, 
stellate,  or  elongated  elements  and  usually  correspond  in 
direction  to  the  lacunae.  The  processes  vary  in  length  and 
form,  and  most  of  them  extend  toward  the  periphery, 
following  the  canaliculi. 

Dental  Pulp. — The  Pulp  is  the  highly  vascular  and  sensi- 
tive mucous  connective  tissue  that  occupies  the  pulp 
cavity,  or  chamber  and  root  canals  and  is  concerned  with 
the  nutrition  and  growth  of  the  tooth.  It  is  composed 
of  cells  and  intercellular  substance  and  contains  blood- 
vessels and  nerves. 


124  ALIMENTARY   TRACT. 

The  cells  are  of  various  varieties,  the  most  important 
of  which  are  the  ODONTOBLASTS.  These  cells  are  found 
upon  the  surface  of  the  pulp  and  form  a  continuous  layer 
of  cells  one  layer  deep.  The  cells  are  elongated  flask- 
shaped  elements  from  which  three  sets  of  processes  extend. 
These  are  dentinal,  pulpal  and  lateral.  The  dentinal  process 
or  processes  arise  from  the  peripheral  end  of  the  cell 
and  extend  into  the  dentinal  tubules,  and  they  have  been 
described  under  the  dentin.  The  lateral  processes  pass 
from  the  sides  of  the  cells  to  the  neighboring  cells,  while 
the  pulpal  processes  extend  from  the  central  ends  of  the 
odontoblasts  to  the  deeper  cellular  elements  of  the  pulp. 
The  nucleus  occupies  the  end  of  the  cell  next  the  pulp 
reticulum.  Beneath  the  layer  of  odontoblasts  there  is 
a  narrow  layer  of  tissue  almost  devoid  of  cells,  then  an 
area  of  which  the  cells  are  quite  numerous,  and  again  a 
region,  the  center  of  the  pulp,  in  which  there  are  very  few 
cellular  elements.  The  cells  are  spindle-shaped,  stellate 
and  spheroid  in  form  and  possess  many  or  few  hair-like 
processes  that  pass  in  all  directions. 

The  ARTERIES,  apical,  of  the  pulp  are  derived  from  a 
branch  that  enters  the  root  canal  of  the  tooth;  as  this 
vessel  passes  toward  the  pulp  chamber  it  gives  off  branches 
that  form  plexuses  parallel  to  the  long  axis  of  the  tooth; 
ultimately  forming  rich  capillary  plexuses  in  the  neighbor- 
hood of  the  odontoblastic  layer.  The  blood  is  collected 
by  venous  channels  that  anastomose  freely  and  empty 
into  one  channel  that  leaves  through  the  root  canal. 

The  NERVES,  one  or  more,  pass  through  the  root  canal 
giving  off  a  few  fibres  here;  in  the  pulp  chamber  branches 
are  distributed  in  every  direction  forming  arch  plexuses, 
after  losing  their  myelin  sheaths,  beneath  the  layer  of 
odontoblasts.  From  this  plexus  fibres  are  said  to  pass 
between  the  odontoblasts  to  end  in  bulbous  enlargements 


TEETH.  125 

within  the  central  ends  of  the  dentinal  tubules.  Magitot 
claims,  however,  that  the  dentinal  fibres  are  continuations 
of  the  nerve  fibres. 

The  Peridental,  or  Alveolodental  membrane,  is  a  highly 
vascular  and  sensitive  white  fibrous  tissue  membrane  that 
lines  the  alveolar  processes  of  the  jaw  and  covers  the  roots 
of  the  teeth.  It  is  thickest  at  gum  and  apical  portions 
and  thinnest  in  the  middle.  The  fibrous  elements  are 
bundles  of  white  fibrous  tissue  that  pass  into  the  cemental 
layers  on  the  one  hand  and  into  the  bony  tissue  of  the 
jaw  on  the  other  hand,  resembling  Sharpey's  fibres.  In 
general  around  the  apex  of  the  tooth  the  fibre  bundles 
are  arranged  fan-like  and  are  directed  upward  and  outward. 
In  the  body  of  the  tooth  the  fibre  bundles  pass  directly 
outward  from  the  cementum  to  the  alveolar  wall  and  are 
largest  and  strongest  here.  At  the  gum  margin  the  fibre 
bundles  pass  outward  and  are  lost  in  the  fibrous  tissue 
of  the  gum,  or  pass  toward  the  adjacent  tooth  as  the 
case  may  be. 

Upon  the  inner  surface  of  the  membrane  are  found  the 
cementoblasts;  these  are  irregular  flattened  elements  possess- 
ing a  clearly  defined  nucleus  and  numerous  delicate 
irregular  processes  that  extend  in  various  directions. 
They  are  evenly  distributed.  Upon  the  opposite  (alveolar) 
surface  of  this  membrane  are  the  osteoblasts  that  form 
the  bone  of  the  jaw.  In  the  meshes  of  the  fibre  bundles 
are  found  fibroblasts  or  connective-tissue  cells  and  some 
osteoclasts  or  bone-destroying  cells.  The  latter  are  large, 
fairly  regular,  oval  or  round  cells  that  possess  several 
nuclei  and  usually  have  no  processes. 

The  arteries  are  derived  from  the  apical  artery  and  pass 
up  parallel  to  the  long  axis  of  the  tooth,  giving  off  branches 
at  intervals;  these  form  capillary  plexuses  beneath  the 
alveolar  and  cemental  side  of  the  membrane.  The  blood 


126  . \I.I.MK.\T.\RY    TRACT; 

is  collected  by  venous  channels  that  ultimately  empty 
into  the  apical  vein. 

The  veins  are  likewise  derived  from  those  at  the  apex 
and  are  distributed  somewhat  like  the  arteries. 

The  functions  of  the  alveolodental  membrane  are  physical 
and  sensor.  It  holds  the  tooth  in  place,  returns  it  to  its 
normal  position  when  slightly  rotated  or  displaced;  upon 
one  side  it  forms  cementum  and  upon  the  other  it  forms 
bone. 

Nasmyth's  Membrane. — This  is  a  thin  indestructible 
membrane  covering  the  enamel  of  the  tooth.  It  is  said 
by  some  to  be  the  remains  of  the  enamel  organ,  while  others 
claim  it  is  a  continuation  of  the  cementum.  The  former 
seems  the  more  probable  origin. 

THE  TONGUE. 

The  Tongue,  like  the  Teeth,  occupies  part  of  the  mouth 
cavity.  It  is  covered  by  a  MUCOUS  MEMBRANE  that  con- 
sists of  stratified  squamous  cells,  basement  membrane  and 
tunica  propria,  which,  along  the  sides  and  base,  is  papilla  ted. 
The  upper  surface,  or  dor  sum,  is  characteristic.  Its  apical 
two-thirds  is  covered  by  minute  projections,  called  papillce; 
of  these  there  are  three  varieties,  FILIFORM,  FUNGIFORM  and 
CIRCUMVALLATE.  The  central  portion  consists  chiefly 
of  voluntary  striated  muscle. 

The  FILIFORM  PAPILLA  are  cone-shaped  projections  of 
the  tunica  propria,  covered  by  the  stratified  squamous  cells, 
the  outer  ones  of  which  are  hard  and  horny.  The  central 
part  of  a  papilla  consists  of  white  fibrous  tissue,  which  is 
thrown  into  small  secondary  papilla  that  are  not  visible 
externally.  These  papillae  are  the  most  numerous,  and  are 
scattered  over  the  whole  of  the  apical  two-thirds.  They 
are  directed  backward,  and  are  the  ones  that  produce  the 


TONGUE.  127 

scratching  sensation  when  the  hand  is  lickea  by  a  lower 
animal. 

The  FUNGIFORM  PAPILLA  are  flat- topped,  table-like 
structures,  in  which  the  sides  are  parallel.  They  have 
secondary  papillae,  and  are  scattered  like  the  filiform  variety, 
but  are  less  numerous. 

The  CIRCUMVALLATE  PAPILLA  are  the  most  important. 
While  the  top  is  flat,  the  sides  usually  converge  and  give 
this  variety  a  narrow  base.  SECONDARY  PAPILLA  are 
found  only  on  the  upper  portion.  Each  papilla  is  sur- 
rounded by  a  little  -vallum,  or  ditch,  hence-the  name. 

These  papillae  are  the  least  numerous,  and  are  found 
only  in  one  area.  Ten  to  fifteen  arrange  themselves  like  a 
letter  V,  with  the  apex  at  the  foramen  cecum,  a  little  de- 
pression that  lies  at  the  boundary  of  the  apical  two-thirds 
and  basal  one- third  of  the  tongue.  These  papillae  contain 
TASTE-BUDS  along  their  sides. 

The  TASTE-BUDS  are  the  organs  of  taste,  lie  in  the  epithelial 
portion  of  the  sides,  and  have  a  definite  structure. 

They  are  barrel-shaped,  and  open  at  the  exposed  ends. 
Each  consists  of  two  kinds  of  cells,  outer  (stave-like),  the 
sustentacular ,  or  supporting  cells,  and  the  inner,  neuro- 
epithelial  elements. 

The  SUSTENTACULAR  cells  are  flat  and  stave-like  elements 
possessing  a  prominent  nucleus.  The  neuro -epithelial 
elements  are  spindle-shaped,  and  each  ends  in  a  minute, 
hair-like  process,  the  gustatory  hair,  that  projects  through 
an  opening  in  the  barrel,  the  gustatory  pore.  The  nerve 
fibre  that  extends  to  each  bud  forms  branches,  one  of  which 
is  supplied  to  each  neuro-epithelial  cell. 

Beneath  the  mucosa  is  found  the  MUSCULATURE  of  the 
tongue.  This  consists  of  the  voluntary  striated  variety, 
arranged  longitudinally,  vertically  and  transversely.  The 
longitudinal  fibres  are  arranged  in  bundles  that  lie  beneath 


128 


ALIMENTARY   TRACT. 


FIG.  44. — CROSS-SECTION  OF  TONGUE. 

a.  Stratified  squamous  cells;  b.  basement  membrane;  c.  tunica  propria;  d. 
serous  glands;  e.  mucous  glands; /.^venule;  g.  longitudinal  muscle  fibres; 
h.  vertical  muscle  fibres;  i.  transverse  muscle  fibres;  /.  septum;  m. 
filiform  papilla;  n.  secondary  papillae;  r.  adipose  tissue.  A.  Filiform 
papilla.  B.  Fungiform  papilla.  C,  D.  Circumvallate  papillae — m,  m. 
taste-buds;  w,  n.  glands.  E.  Taste-bud — o.  nucleus  of  neuro-epithelial 
cell;  r.  nerve  fibre;  s.  gustatory  hair;  t.  sustentacular  cell;  v.  neuro- 
epithelial  cell. 


TONSILS.  129 

the  tunica  propria  and  extend  around  the  tongue.  They  are 
separated  by  small  bundles  of  vertical  fibres.  In  the  center, 
the  fibres  are  vertical,  oblique  and  transverse,  and  are 
separated  in  the  middle  line  by  a  little  partition,  or  septum. 
This  consists  of  white  fibrous  tissue,  and  arises  at  the  base, 
but  does  not  reach  the  tip.  It  varies  in  height,  being  higher 
in  the  middle  than  at  either  end.  In  the  muscular  portion, 
small  glands  afe  often  found.  Occasionally,  branched 
muscle  fibres  are  found. 

The  true  base  of  the  tongue,  the  posterior  one-third, 
possesses  no  papilla.  It  contains  small  salivary  glands  and 
collections  of  lymphoid  tissue  called  the  lingual  tonsils. 

The  blood-vessels  are  quite  numerous;  the  capillaries  ex- 
tend into  the  papillae  and  between  the  muscle  fibres  and 
form  plexuses  around  the  glands. 

The  lymphatics  are  in  the  base,  and  are  found  quite 
numerous  in  the  tunica  propria,  where  they  receive  branches 
from  the  papillae. 

THE  TONSILS. 

The  Tonsils  are  found  just  between  mouth  and  pharynx, 
and  are  essentially  lymphoid  structures. 

They  are  covered,  upon  their  exposed  surface,  by  strati- 
fied squamous  cells  that  dip  down  into  the  organ  in  the  form 
of  irregular  tubes  called  the  tonsillar  crypts.  The  organ  is 
separated  from  the  surrounding  tissue  by  a  layer  of  white 
fibrous  tissue,  the  capsule,  that  sends  in  trabeculae,  which 
form  the  main  framework  of  the  organ.  Th/bulk  of  the 
tonsil  consists  of  lymphoid  tissue,  in  the  form  of  the  diffuse 
variety  and  solitary  follicles.  The  latter  show  germinal  cen- 
ters, and  are  found  chiefly  around  the  crypts.  The  support- 
ive tissue  is  of  the  retiform  -variety.  Leukocytes  may  be 
seen  on  their  way  to  the  crypts,  where  they  become  the 
salivary  corpuscles. 
9 


130  ALIMENTARY    TRACT. 

Blood-vessels,  and  especially  lymphatics,  are  numerous. 
The  vascular  capillaries  ramify  the  lymphoid  tissue,  while  the 
lymph  channels  surround  the  follicles  and  form  a  peripheral 
vessel  beneath  the  fibrous  capsule. 


'/  ;£ 


4 

FIG.  45. — VERTICAL  SECTION  OF  HUMAN  TONSIL. 

a.  Stratified  squamous  epithelium;  b.  basement  membrane;  c.  tunica  propria; 
d.  trabecuke;  e.  diffuse  lymphoid  tissue; /.  adipose  tissue;  h,  capsule;  /. 
glands;  k.  muscle;  /.  blood-vessel;  ;;/.  epithelium  of  crypts:  (/,  q.  crypts. 

THE  PHARYNX. 

The  Pharynx  is  a  musculo -membranous  bag  that  connects 
the  mouth  cavity  and  the  esophagus.  It  has  three  coats, 
MUCOUS,  FIBROUS  and  MUSCULAR. 

The  MUCOUS  COAT  is  lined,  in  the  lower,  or  alimentary 
portion,  by  stratified  squamous  cells.  The  upper,  or  res- 
piratory, part  is  lined  by  stratified  ciliated  cells.  These  all 
rest  upon  a  basement  membrane,  beneath  which  is  the  tunica 
propria,  that  is  thrown  into  waves  or  papilla?.  The  tunica 


ESOPHAGUS.  131 

propria  contains  a  considerable  amount  of  difTase  lymphoid 
tissue. 

The  FIBROUS  COAT  is  composed  of  large  bundles  of  white 
fibrous  tissue,  and  serves  as  a  support  to  the  larger  vessels 
and  the  small  pharyngeal  glands.  It  also  serves  as  an  attach- 
ment for  the  muscle  fibres. 

The  MUSCULAR  COAT  consists  of  voluntary  striated  muscle, 
surrounded  externally  by  loose  areolar  tissue. 

The  blood-vessels  and  lymphatics  are  numerous.  The  cap- 
illaries are  found  in  the  mucous  and  muscular  coats,  around 
the  glands  and  between  the  muscle  fibres. 

ESOPHAGUS. 

The  remainder  of  the  Alimentary  Tract  is  tubular,  and 
possesses  four  coats,  MUCOUS,  SUBMUCOUS,  MUSCULAR  and 
FIBROUS.  The  MUCOSA  is  further  subdivided  into  four 
layers,  epithelium,  basement  membrane,  tunica  propria  and 
muscularis  mucoscz. 

In  the  Esophagus,  the  MUCOUS  COAT  is  lined  by  stratified 
sqamous  cells.  These  rest  upon  the  basement  membrane, 
beneath  which  is  the  papillated  tunica  propria.  The  latter 
consists  of  yellow  elastic  and  white  fibrous  tissues,  in  which 
the  capillary  vessels  form  a  delicate  network  beneath  the 
epithelium;  the  ducts  of  the  glands  pass  through  this  layer 
on  their  way  to  the  surface.  The  muscularis  mucoscz  con- 
sists of  involuntary,  nonstriated  muscle  fibres,  circularly  and 
longitudinally  arranged.  In  the  upper  portion  of  the 
esophagus,  this  layer  is  often  wanting,  but  in  the  lower 
part  it  is  always  present.  In  the  relaxed  condition,  the 
mucous  and  submucous  coats  are  thrown  into  longitu- 
dinal folds. 

The  SUBMUCOUS  COAT  is  composed  of  coarser  bundles  of 
white  fibrous  tissue,  which  forms  a  loose  network  for  the 


132 


ALIMENTARY    TRACT. 


support  of  the  large  blood-vessel  trunks.  In  this  coat  are 
seen  a  number  of  glandular  structures,  the  esophageal 
glands,  which  are  apparently  mucous,  as  they  stain  lightly. 
They  send  their  ducts  through  the  mucous  coat.  As  the 


FIG.  46. — CROSS-SECTION  ESOPHAGUS. 

a.  Stratified  squamous  epithelium;  b.  basement  membrane;  c.  tunica  propria: 
d.  muscularis  mucosae;  e.  esophageal  gland;  /.  blood-vessel;  g.  sub- 
mucosa;  k.  outer  longitudinal  muscle;  /.  fibrous  coat;  n.  inner  circular 
muscle. 

stomach  is  approached,  these  glands  become  more  numerous, 
and  may  even  be  found  in  the  mucosa. 

The  MUSCULAR  COAT  consists  of  muscle  fibre,  arranged  in 
two  layers,   inner  circular  and  outer  longitudinal.     In  the 


STOMACH.  133 

upper  third,  these  fibres  are  of  the  voluntary  striated  variety, 
in  the  lower  third,  smooth,  and  in  the  middle  portion,  mixed. 
The  involuntary  variety  continues  throughout  the  remainder 
of  the  tract. 

The  FIBROUS  COAT  consists  of  fibre-elastic  tissues,  and 
connects  the  organ  with  surrounding  tissues.  It  sends  in 
bundles  between  the  muscle  bundles,  of  which  they  are  said 
to  form  the  perimysium. 

The  blood-vessels  pass  directly  to  the  submucosa,  where 
branches  are  formed,  and  sent  to  the  mucous  and  muscu- 
lar coats.  Here  they  form  longitudinal  plexuses. 

The  lymphatics  follow  the  same  general  course. 

The  nerves  end  in  the  muscular  coat  and  beneath  the 
epithelial  cells.  Others  surround  the  glands. 

STOMACH. 

The  Stomach  is  the  first  part  of  the  tract  in  which  the 
food  rests  for  any  length  of  time,  and  in  which  active  diges- 
tion and  absorption  occur.  Although  very  large,  it  still 
represents  a  tube,  and  has  the  four  coats  above  mentioned. 
It  is  divided  into  three  portions,  the  CARDIA,  FUNDUS  and 
PYLORIC  END.  They  pass  into  one  another  insensibly, 
and  the  structure  of  the  first  two  parts  is  practically  the 
same. 

The  MUCOUS  COAT  presents  a  great  change  over  that  of 
the  esophagus,  showing  a  higher  degree  of  specialization. 
In  it  are  seen,  with  the  naked  eye,  a  number  of  minute 
depressions,  the  gastric  crypts,  or  pits,  from  which  the  gas- 
tric glands  extend  into  the  deeper  portions.  Between  or 
bounding  the  pits,  are  the  inter  glandular  projections.  Each 
gland  consists  of  mouth,  neck  and  fundus,  or  secretory  por- 
tion, and  is  lined  by  simple  epithelial  cells. 

The  cells  rest  upon  a  basement  membrane,  which,  in  turn, 


134  ALIMENTARY    TRACT. 

rests  upon  the  tunica  propria.  The  latter  forms  the  core  of 
the  interglandular  projeetions  that  form  the  boundaries  of 
the  pits.  Between  the  glands,  the  tunica  propria  consists  of 
narrow  bands  of  the  fibrous  tissue,  which  contains  a  great 
deal  of  diffuse  lymphoid  tissue,  bundles  of  muscle  fibres 
from  the  muscularis  mucosae,  and  capillaries,  both  vascular 
and  lymphatic,  in  great  numbers.  In  places,  the  lymphoid 
tissue  is  collected  into  solitary  follicles  that  are  lens-shaped, 
and  are  called  the  lenticular  follicles,  or  glands.  These  are 
numerous  in  the  pyloric  end.  The  MUCOSA  is  bounded  ex- 
ternally by  the  muscularis  mucosce,  which  consists  of  two 
layers  of  smooth  muscle  fibres,  arranged  as  inner  circular 
and  outer  longitudinal  bands. 

In  the  cardiac  and  fundal  portions,  the  secretory  portions 
of  the  glands  are  chiefly  of  the  simple  tubular  variety.  The 
mouth  is  short,  with  the  neck  and  fundus  of  about  the  same 
length.  In  the  neck  and  fundus,  are  found  two  varieties  of 
low  columnar  cells,  the  chief,  peptic,  or  adelomorphous  cells, 
and  the  large  delomorphous,  acid,  oxyntic,  or  acid  cells. 

The  peptic  cells  are  low  columnar  elements,  and  are  found 
more  numerous  in  the  fundus  than  in  the  neck.  The 
nucleus  is  usually  circular  or  oval,  and  takes  the  stain  very 
well.  These  cells,  in  the  glands,  have  an  affinity  for  the 
hematoxylin,  and  appear  bluish  when  characteristically 
stained.  They  also  line  the  mouth  and  pits,  and  cover  the 
interglandular  projections.  In  these  places,  the  cells  be- 
come very  much  longer,  and  take  the  stain  but  faintly. 
They  form  a  broad  band  of  palely  stained  protoplasm,  in 
which  the  darkly  stained  nuclei  have  a  basal  location, 
forming  a  row  of  closely-placed  bodies.  The  lateral  bound- 
aries are  not  distinct,  but  the  nuclei  indicate  the  breadth 
of  the  cell.  Altogether,  they  give  a  feather-like  appearance 
to  the  interglandular  projections.  Besides  the  peptic  cells, 
a  few  goblet  cells  are  found  in  the  latter  region. 


STOMACH. 


The  acid  cells  are  readily  distinguished  frorfl  the  others  by 
their  size,  shape,  and  affinity  for  acid  stains.  They  are  very 
large,  oval,  or  triangular  elements,  most  numerous  in  the 


FIG.  47. — CROSS-SECTION  OF  SEGMENT  OF  STOMACH. 

A.  Cardiac  Region — a.  mucous  coat;  b.  submucous  coat;  c.  muscular  coat; 
d.  fibrous  coat;  e.  epithelium;/,  interglandular  projection;  g.  basement 
membrane;  h.  gastric  pit;  i.  neck  of  gland;  k.  acid  cell;  /.  tunica  propria; 
m,  n.  layers  of  muscularis  mucosae;  o.  submucosa;  p.  circular  layer  of 
muscular  coat;  q.  longitudinal  layer  of  muscular  coat;  r.  oblique  layer 
of  muscular  coat;  s.  white  fibrous  tissue  layer  containing  the  nerve  plexus 
of  Auerbach.  B.  Gland  of  Cardiac  Region  of  Stomach — a.  gastric  pit; 
b.  columnar  epithelium;  c.  goblet  cell;  d.  basement  membrane;  e.  tunica 
propria  of  interglandular  projection;  /.  neck  of  gland;  g.  acid  cell;  h. 
peptic  cell. 

necks,  but  also  scattered  in  the  fundus.     They  are  found 
along  the  wall  of  the  tubule,  and  usually  beneath  the  peptic 


136  ALIMENTARY    TRACT. 

cell,  hence  the  term  parietal,-  or  wall,  cell.  The  nucleus  is 
quite  large,  and  centrally  located,  and  the  protoplasm  con- 
tains minute  canals.  The  affinity  for  acid  stains  is  pro- 
nounced. With  eosin,  they  are  distinctly  red,  while  with 
acid  fuchsin  they  are  colored  a  very  much  deeper  red. 
These  cells  are  supposed  to  form  the  hydrochloric  acid. 

In  the  first  portion  of  the  FUNDUS,  the  glands  are  chiefly 
of  the  simple  tubular  variety.  As  the  PYLORIC  end  is  ap- 
proached, the  branched  tubulars  begin  to  increase,  so  that 
they  form  the  predominating  variety  in  this  end.  There  is 
also  a  marked  change  in  the  lining  cells.  The  acid  cells  be- 
come rapidly  fewer  in  number,  and,  in  the  pyloric  end,  are 
but  seldom  seen.  One  can,  therefore,  be  safe  in  saying 
that  a  section  containing  a  number  of  acid  cells  is  from  the 

FUNDUS,  Or  CARDIA. 

In  the  PYLORIC  END,  the  glands  are  different.  The 
mouth  becomes  longer  and  wider,  and  the  fundus  and  iurk 
comparatively  shorter.  The  lumen  of  the  fundus  is  broader, 
and  the  cells  are  only  of  the  peptic  -variety.  These  cells  are 
usually  longer  and  broader  than  those  in  the  cardiac  glands, 
and  have  distinct  cell  boundaries  and  prominent  basal 
nuclei.  The  protoplasm,  however,  does  not  respond  well 
to  the  stain,  but  is  always  pale.  As  the  pylorico-duodenal 
junction  is  reached,  the  glands  become  shorter  and  less 
numerous,  and  some  may  even  extend  into  the  submucosa. 
The  inter  glandular  projections  become  longer,  and  resemble, 
somewhat,  the  VILLI  of  the  small  intestine. 

The  MUCOSA  and  SUBMUCOSA  are  thrown  into  large  folds, 
the  rug(E.  These  folds  and  glands  increase  greatly  the  ab- 
sorptive and  secretory  surfaces. 

The  SUBMUCOUS  COAT  consists  of  loosely  arranged  white 
fibrous  tissue,  in  which  the  larger  blood-vessels  are  seen. 

The  MUSCULAR  COAT  is  composed  of  smooth  muscle  ar- 
ranged into  three  layers.  Of  these,  the  inner  is  oblujm  ; 


STOMACH. 


137 


the  middle,  circular,  and  the  outer,  longitudinal.  At  both 
openings  of  the  stomach,  the  circular  fibres  are  more 
numerous,  and  form  sphincters.  Of  these  the  sphincter 
pylori  is  the  more  prominent. 

The  FIBROUS,  SEROUS  or  PERITONEAL  COAT  is  composed  of 
a  thin  layer  of  white  fibrous  tissue,  covered  by  a  reflection  of 
the  peritoneum. 


FIG.  48. — LONGITUDINAL  SECTION  OF  SEGMENT  OF  PYLORIC  REGION  OF 

STOMACH. 
a.  Mucous  coat;  b.  submucous  coat;  c.  muscular  coat;  d.  fibrous  coat;  e. 

interglandular  projection;  /.   epithelium;   g.   basement  membrane;   h. 

gastric  pit;  i.  pyloric  glands;  k.  tunica  propria;  /.  muscularis  mucosae; 

m.  blood-vessel;  n.  connective  tissue  in  muscular  coat;  o.  inner  circular 

layer  of  muscle;  p.  outer  longitudinal  layer  of  muscle. 

Throughout  the  alimentary  tract,  the  chief  vessels  are 
found  in  the  submucosa,  and  from  this  coat,  the  branches 
are  sent  to  the  mucosa  and  muscularis.  In  the  stomach, 
the  vascular  and  lymphatic  capillaries  are  very  numerous 
in  the  tunica  propria.  The  lymphatics  empty  into  larger 
vessels  in  the  submucosa,  in  which  the  veins  also  are 
formed. 


138  ALIMENTARY    TRACT. 

The  nerves  are  chiefly  sympathetic,  and  are  arranged  in 
two  plexuses,  one  in  the  submucosa,  and  the  other  in  the 
muscular  coat.  (See  Intestine,  p.  146). 

SMALL  INTESTINE. 

The  Intestinal  Tract  consists  of  two  main  portions,  the 
Small  and  Large  Intestines.  These  each  have  their  sub- 
divisions, which  usually  differ  from  one  another. 

The  Small  Intestine  is  divided  into  DUODENUM,  JEJUNUM 
and  ILEUM.  They  all  have  the  same  general  structure. 
This  will  first  be  described,  and  then  the  differences  studied. 

There  are  four  coats,  mucosa,  submucosa,  muscularis 
and  fibrosa,  or  serosa. 

The  MUCOSA  has  four  layers,  epithelium,  basement  mem- 
brane, tunica  propria  and  muscularis  mucosce.  It  contains 
a  large  number  of  simple  tubular  glands,  the  crypts  of  Lieber- 
kuehn,  or  intestinal  crypts.  Above  the  level  of  the  glands, 
the  mucosa  is  thrown  into  an  immense  number  of  small, 
finger-like  projections,  the  mlli. 

The  epithelium  is  chiefly  of  the  simple  columnar  variety, 
with  varying  numbers  of  goblet  cells.  Those  within  the 
gland  are  nearly  conical  in  shape,  and  stain  darkly.  The 
protoplasm  is  granular,  and  the  nucleus  basal.  Upon  the 
villi,  the  cells  are  columnar,  and  the  protoplasm  granular 
and  reticular,  while  the  exposed  margin  is  differentiated 
into  a  cuticular  border.  Some  hold  that  the  cells  in  the 
glands  secrete  a  fluid  used  in  digestion;  others  consider 
them  goblet  cells  in  different  stages  of  secretory  activity. 

The  goblet  cells  are  distinctly  columnar  elements,  in  which 
the  position  of  the  nucleus  varies  with  the  state  of  secretion. 
They  form  the  mucin.  The  protoplasm  is  granular  and 
reticular,  and,  when  mucin  is  forming,  shows  small  clear 
areas;  these  fuse  to  form  a  single  large  drop  of  mucin  that 


SMALL    INTESTINE. 


139 


forces  the  protoplasm  and  nucleus  to  the  basal  portion  of 
the  cell.  The  sides  are  curved,  producing  the  goblet  form. 
When  the  cuticular  border  ruptures,  and  the  mucin  is 
discharged,  the  cell  becomes  slender  and  irregular.  These 
cells  are  found  mostly  upon  the  villi,  and  become  more 
numerous  as  the  large  intestine  is  approached. 

The  tunica  propria  consists  of  delicate  white  fibrous  tissue 

657 


W  4 


FIG.  49. — CROSS-SECTION  OF  DUODENUM. 

i.  Mucous  coat;  2.  submucous  coat;  3.  muscular  coat;  4.  fibrous  coat;  5,  6. 
villi;  7.  epithelium  of  villus;  8.  muscularis  mucosae;  9.  glands  of  Brunner. 

that  forms  the  core  of  the  villi.  It  contains  diffuse  lym- 
phoid  tissue  and  capillary  vessels,  both  lymphatic  and 
vascular. 

The  muscularis  mucosce  consists  of  two  layers  of  smooth 
muscle  fibres  arranged  circularly  and  longitudinally.  From 
it  bundles  are  sent  up  into  the  villi. 

A  VILLUS  is  a  finger-like  projection  of  the  tunica  propria, 
covered  by  a  basement  membrane-  and  epithelial  cells  of  the 
simple  columnar  and  goblet  varieties.  The  tunica  propria 


140 


ALIMENTARY    TRACT. 


forms  the  core,  and  contains  considerable  diffuse  lymphoid 
tissue,  a  large  number  of  capillary  blood-vessels,  muscle 
fibres  and  a  space  in  the  center  called  the  lacteal.  It  is  by 


FIG.  50. — LONGITUDINAL  SECTION  OF  THE  UPPER  PART  OF  A  VILLUS  OF  A 

DOG. 

a.  Epithelium;  b.  tunica  propria;  c.  capillary;  d.  cuticular  border  of  the 
epithelium;  e.  nucleus  of  wandering  leukocyte;  /.  section  of  goblet 
cell;  g.  mucoid  area  of  goblet  cell;  h.  lacteal;  i.  smooth  muscle  fibre 
(Stohr's  Histology). 

the  villi  that  nature  increases  enormously  the  absorptive 
surface.  The  lacteal  is  the  starting  point  of  the  lymphatic 
system  of  the  intestine. 


SMALL   INTESTINE.  141 

The  lymphoid  tissue  is  often  collected*  into  solitary 
follicles  that  are  usually  present  in  the  mucosa,  and  in  such 
areas  the  glands  and  villi  are  generally  absent. 


FIG.  51. — CROSS-SECTION  OF  ILEUM. 

(7.  Villus;  b.  epithelium;  c.  tunica^  propria  of  villi;  d.  intestinal  gland;  e 
tunica  propria;/,/.  muscularis  mucosae;  g.  blood-vessel;  h.  submucosa; 
i.  circular  muscle  layer;  k.  longitudinal  muscle  layer;  /.  peritoneal  layer; 
w.  fibrous  coat;  ;/.  follicles  of  the  Peyer's  patch. 

The   mucosa   and   submucosa   are    thrown   into   circular 
folds.     These  are  the  valvula  conniventes,  or  folds  of  Kerk- 


142  ALIMENTARY    TRACT. 

ring.  They  are  seen  upon  longitudinal  section  of  the 
bowel. 

The  SUBMUCOSA  consists  of  loose  bundles  of  white  fibrous 
tissue,  and  here  are  to  be  found  the  main  vascular  and 
lymphatic  trunks.  It  enters  into  the  formation  of  the 
valvulce  conniventes,  and  contains  the  duodenal  glands 
of  the  duodenum,  and  the  Peyer's  patches  of  the  ileum. 

The  MUSCULAR  COAT  is  composed  of  inner  circular  and 
outer  longitudinal  layers.  These  are  well  developed  in  the 
duodenum,  but  become  thinner  as  the  colon  is  approached. 

The  fibrous  coat  is  thin,  and  nearly  the  whole  of  the 
intestine  is  covered  by  peritoneum,  forming  a  serous  coat. 

The  JEJUNUM  contains  no  special  structures. 

The  ILEUM  is  characterized  by  agminated  follicles,  or 
Peyer's  patches.  These  are  collections  of  solitary  follicles 
(10  to  60),  generally  found  in  both  the  mucosa  and  submu- 
cosa.  Each  follicle  usually  shows  a  germinal  center. 

The  DUODENUM  is  characterized  by  the  presence  of  a 
large  number  of  branched  tubular  glands  in  its  submucosa. 
The  excretory  ducts  open  at  the  bases  of  the  villi,  and  pour 
their  secretion  into  the  lumen  of  the  intestine.  These  are 
the  duodenal  glands,  or  glands  of  Brunner,  and  they  give 
rise  to  the  succus  entericus. 

LARGE  INTESTINE. 

This  consists  of  Cecum,  Colon,  Rectum  and  Appendix. 
The  structure  of  all  is  practically  the  same. 

The  MUCOSA  contains  simple  tubular  glands,  crypts  of 
Lieberkuehn,  which  are  usually  short,  and  broader  than 
those  of  the  small  intestine.  The  cells  lining  these  are 
goblet  cells.  The  tunica  propria  contains  a  great  deal  of 
diffuse  lymphoid  tissue  that  is  often  collected  into  solitary 
follicles  that  show  germinal  centers.  Vahnlcr  connivcntcs 
and  mill  are  absent. 


LARGE    INTESTINE.  143 

The  outer  three  coats  are  like  those  of  the  small  intestine, 
except  for  difference  in  the  muscular  coat.  The  longitu- 
dinal fibres  are  usually  arranged  into  three  bands,  the 
t&nicecoli,  which  are  about  one-sixth  shorter  than  the  bowel. 
These  act  as  a  purse  string  to  the  intestine,  and  cause  it  to 
be  thrown  into  a  number  of  speculations.  If  the  bands 
be  removed,  the  sacculations  disappear. 


FIG.  52. — CROSS-SECTION  OF  SEGMENT  OF  COLON. 

a.  Mucous  coat;  b.  submucous  coat;  c.  muscular  coat;  d.  fibrous  coat;  e. 
columnar  cell;/,  goblet  cell;  g.  basement  membrane;  h.  tunica  propria;  /. 
inner  circular  layer  of  muscularis  mucosae;  k.  outer  longitudinal  layer 
of  muscularis  mucosae;  /.  inner  circular  layer  of  muscular  coat;  m.  outer 
longitudinal  layer  of  muscular  coat. 

The  Rectum  has  its  mucous  and  submucous  coats  formed 
into  folds  called  the  rectal  valves.  These  contain  a  continua- 
tion of  the  muscular  coat,  by  means  of  which  the  valves 
may  be  protruded  into  the  lumen.  At  the  lower  end,  the 
ANUS,  stratified  squamous  cells  replace  the  simple  columnar, 
and  this  marks  another  muco -cutaneous  junction  as  in  the  lips. 

The  Appendix  is  a  continuation  of  the  cecutn.     It  has  the 


144  ALIMENTARY   TRACT. 

four  coats,  MUCOSA,  SUBMUCOSA,  MUSCULARIS  and  FIBROSA, 
or  SEROSA. 

The  MUCOSA  is  usually  irregular,  and  consists  of  simple 
columnar  epithelial  cells  that  rest  upon  a  basement  mem- 
brane; beneath  the  latter  lies  the  tunica  propria,  which  is 
bounded  by  the  muscularis  mucosce. 

In  the  MUCOSA  are  a  large  number  of  tube-like  depressions, 
the  glands  of  Lieberkuehn.  These  possess  an  equal  diameter 
throughout,  and  are  quite  regularly  distributed.  The  cells 
of  the  mucosa  are  the  simple  columnar  variety,  interspersed 
with  many  goblet  cells.  They  are  quite  distinct,  and  usually 
possess  a  basal  border.  The  cells  in  the  base  of  the  glands 
supply  the  parts  higher  up,  and  are  consequently  the  young- 
est. The  glands  are  about  25,000  (Kelly  and  Hurdon)  in 
number,  and  are  absent  where  the  solitary  follicles  are  found. 

The  tunica  propria  consists  of  a  delicate  fibre-elastic 
stroma  containing  many  capillaries,  considerable  diffuse 
lymphoid  tissue  and  solitary  follicles  (often  300  to  400  in  num- 
ber). The  solitary  follicles  contain  germinal"  centers,  and 
may  extend  into  the  submucosa.  Immediately  over  them, 
the  glands  are  usually  absent. 

The  muscularis  mucosa  is  not  always  present.  It  consists 
of  smooth  muscle  fibres  forming  a  thin  band  separating  the 
mucosa  from  the  submucosa. 

The  SUBMUCOSA  consists  of  loose  white  fibrous  tissue,  and 
supports  the  larger  blood-vessels.  In  older  subjects,  it 
becomes  thicker  and  denser,  and  passes  into  the  tunica 
propria. 

The  MUSCULAR  coat  is  usually  separable  into  two  distinct 
layers,  inner  circular  and  outer  longitudinal.  The  former 
is  the  more  prominent,  and  extends  to  the  blind  end,  where 
the  fibres  form  a  dome-like  collection  of  interlacing  fibres. 
The  longitudinal  fibres  are  less  prominent  than  the  circular. 
Both  layers  are  pierced,  at  intervals,  by  large  vessels.  Such 


APPENDIX. 


an  opening,  of  which  one  especially  exists  at  the  blind  end, 
is  called  an  HIATUS   (Kelly  and  Hurdon). 


FIG.  53. — CROSS-SECTION  OF  HUMAN  APPENDIX. 

a.  Lumen;  b.  epithelium;  c.  basement  membrane;  d.  glands;  e.  tunica  propria; 
/.  diffuse  lymphoid  tissue;  g.  muscularis  mucosae;  h.  solitary  follicle;  i. 
adipose  tissue;  k.  submucosa;  /  circular  muscle  fibres;  m.  longitudinal 
muscle  fibres;  n.  fibrous  coat. 

The  SEROUS  coat  consists  of  white  fibrous  tissue,  sur- 
rounded by  the  peritoneum. 

The  lumen  tends  to  disappear  more  frequently  than  sup- 
posed; this  change  occurs  during  the  ages  ranging  from  20 
to  80.  The  older  the  individuals,  the  higher  the  percent- 


146  ALIMENTARY    TRACT. 

age  of  occlusions.  The  glands  are  gradually  destroyed  by 
the  thickening  of  the  submucosa,  this  process  beginning  at 
the  blind  extremity  and  proceeding  toward  the  bowel. 
Occasionally,  in  this  process  of  occlusion,  quite  an  abun- 
dance of  adipose  tissue  is  seen  in  the  submucosa. 

The  chief  blood-vessels  of  the  intestines  pass  from  between 
the  layers  of  the  mesentery  into  the  submucosa.  From 
these  trunks,  branches  are  sent  to  the  various  coats.  In  the 
villi,  dense  capillary  plexuses  are  formed  around  the  lacteals, 
and,  lower  down  in  the  mucosa,  around  the  gland.  The  blood 
is  returned  to  the  submucosa  through  venous  channels,  and 
.  these  unite  here  to  form  the  main  venous  trunks  that  leave 
the  intestine  to  pass  between  the  layers  of  the  mesentery. 

The  lymphatics  of  the  intestine  start  as  the  lacteals. 
These  pass  from  the  apices  of  the  villi  to  the  bases,  where 
they  open  into  a  set  of  vessels  near  the  muscularis  mucosae. 
From  this  plexus,  vessels  connect  with  another  network 
in  the  submucosa.  The  latter  receives  lymph  through  other 
vessels  that  encircle  the  solitary  follicles  and  patches.  From 
this  submucous  plexus,  vessels  pierce  the  muscular  coat  to 
pass  between  the  layers  of  the  mesentery,  receiving,  at  the 
same  time,  branches  from  the  muscularis  itself.  Ulti- 
mately, these  channels  empty  into  the  receptaculum  chyli. 
The  chyle  vessels,  or  lacteals,  are  usually  guarded,  at  the 
base,  by  a  valve  that  prevents  regurgitation,  and  aids  in 
producing  a  vacuum  in  the  lacteals,  thus  aiding  absorption. 
The  nerves  are  chiefly  sympathetic  and,  as  in  the  stomach, 
two  plexuses  are  formed.  The  plexus  of  Meissner  lies  in  the 
submucosa,  and  that  of  Auerbach  in  the  muscular  coat,  be- 
tween the  circular  and  longitudinal  layers.  Where  the 
plexus  fibres  join,  little  collections  of  multipolar  cells,  called 
ganglia,  are  formed.  The  plexus  of  Meissner  seems  to  be 
a  derivative  of  the  plexus  of  Auerbach.  The  mucosa  is  sup- 
plied by  fibres  from  the  former. 


CELLS    LINING    ALIMENTARY    TRACT.  147 

The  cells  lining  the  various  portions  of  the  Alimentary 
Tract  are  as  follows. 
LIPS   ..............   Stratified  squamous. 

MOUTH  .............   Stratified  squamous. 

TONGUE  .............   Stratified  squamous. 

PHARYNX  ............  Stratified  squamous. 

ESOPHAGUS    ...........  Stratified  squamous. 

(  Acid  cells. 
Peptic  cells. 


STOMACH 


CARDIAC  END   ...>>„„      . 

Tall  columnar. 

[  Goblet  cells  (a  few) . 
f  Peptic  cells. 

PYLORIC  END  «...-<  Tall  columnar. 

Goblet  cells. 


f  Simple  columnar. 
SMALL  INTESTINE  . 

(  Goblet  cells. 

f  Goblet  cells. 
LARGE  INTESTINE  .  .    .  <  «. 

[  Simple  columnar. 

ANUS      .............   Stratified  squamous. 

The  differences  between  the  Small  and  Large  Intestines 
are  as  follows  : 

SMALL.  LARGE. 

GLANDS.  LONG  AND  NARROW.        BROAD. 

CELLS.  CHIEFLY  CHIEFLY 

GLANDULAR.  GOBLET. 

VILLI.  PRESENT.  ABSENT. 

VALVUL^.  PRESENT.  ABSENT. 

BRUNNER'S  GLANDS.        PRESENT.  ABSENT. 

PEYER'S  PATCHES.  PRESENT.  ABSENT. 

LONGITUDINAL  ABSENT.  PRESENT. 

BANDS. 

SACCULATIONS.  ABSENT.  PRESENT. 


CHAPTER  X. 


THE  DIGESTIVE  GLANDS. 

The  Digestive  Glands  are  the  Liver,  and  Salivary  Glands, 
the  Parotid,  Pancreas,  Sublingual  and  Submaxillary. 

LIVER. 

The  Liver,  the  largest  gland  in  the  body,  is  compound 
tubular  in  structure.  It  is  surrounded  by  a  sheath  of  white 
fibrous  tissue,  the  capsule  of  Glisson,  which  is  covered  by 
peritoneum.  On  the  under  surface  of  the  organ,  the  capsule 
follows  the  blood-vessels  at  the  portal  or  transverse  fissure 
into  the  gland,  and  forms  the  interlobular  connective  tissue. 
Folds  and  bands  form  the  various  ligaments,  suspensory, 
coronary  and  lateral.  The  round  ligament  is  formed  by  the 
persistent,  closed  umbilical  vein. 

The  Liver  is  divided  into  LOBES  and  LOBULES,  of  which 
the  latter  represent  the  UNITS.  A  description  of  a  lobule 
will  suffice  for  that  of  the  whole  liver. 

Each  Lobule  consists  of  a  collection  of  RADIATING  CHAINS 
of  HEPATIC  CELLS,  the  TUBULES,  that  start  from  the  CENTRAL, 
or  INTRALOBULAR  VEIN.  These  CHAINS  are  separated  from 
one  another  by  reticulum,  which  supports  the  cells  and  the 
INTRALOBULAR  BLOOD  CAPILLARIES;  these  capillaries  are  of 
the  sinusoidal  variety;  that  is,  the  endothelium  is  attached 
to  the  epithelium  of  the  tubules.  Each  CHAIN  consists  of 
two  or  three  cells  side  by  side,  enclosing  a  small  capillary 
space  called  the  BILE  CAPILLARY.  Peripherally,  the  lobules 
are  not  separated  from  one  another  by  connective  tissue, 
except  in  the  pig  and  camel.  In  these  animals,  the  lobules 

148 


LIVER.  149 

are  sharply  outlined  by  bands  of  connectiw  tissue.     This 


FIG.  54. — LIVER  OF  PIG. 

a.   Interlobular  connective  tissue  containing  a  portal  system  consisting  of 
'  b.  Interlobular  branch  of  hepatic  artery. 

c.  Interlobular  branch  of  portal  vein. 
v  d.  Interlobular  branch  of  bile  duct. 
e.  chains  of  hepatic  cells;/,  central  vein;  g.  chain  of  cells  highly  magnified. 

occurs  somewhat  imperfectly  in   the   human  liver  under 
pathologic  conditions  (chronic  interstitial  hepatitis). 


150  TIIK    DIGESTIVE    GLANDS. 

According  to  Mall,*  the  lobule,  as  now  considered,  is 
not  the  structural  unit  of  the  liver;  the  structural  unit 
refers  to  all  the  tissue  that  surrounds  each  terminal  branch 
of  the  portal  vein. 

The  HEPATIC  CELLS  are  large,  mononuclear  masses  of  pro- 
toplasm, although  occasionally  two  nuclei  may  be  present. 
The  protoplasm  is  granular,  and  may  contain  droplets  of 
fat,  glycogen  and  even  pigment  granules.  The  cells  are 
traversed  by  minute  canals,  SECRETORY  CAPILLARIES,  that 
open  into  the  bile  capillaries  lying  between  the  cells.  These 
cells  are  arranged  in  irregular  chains  that  consist  of  two 
or  three  cells,  in  cross-section,  and  extend  from  the  central 
vein  to  the  periphery  of  the  lobule.  Such  are  the  HEPATIC 
TUBULES. 

The  BILE  CAPILLARIES,  that  lie  between  the  cells,  are 
merely  notches  in  the  apposed  cells.  They  start  blindly 
at  the  central  vein,  pass  to  the  periphery,  and  empty  into 
INTERLOBULAR  VESSELS  that  possess  a  low  columnar  epithelial 
lining  supported  by  basement  membrane  and  tunica  propria. 
These  unite  to  form  larger  vessels  that  are  lined  by  tall 
columnar  cells.  The  interlobular  ducts  that  lie  between 
the  lobules  are  lined  by  the  same,  and  possess,  in  addition, 
some  muscular  tissue. 

The  INTERLOBULAR  CONNECTIVE  TISSUE  is  seen  in  abun- 
dance, at  times,  at  the  junction  of  several  lobules.  In  such 
areas  will  be  found  branches  of  the  hepatic  artery  and  -vein, 
portal  -vein  and  bile  duct.  These  vessels,  with  the  connective 
tissue,  form  a  PORTAL  SYSTEM,  or  CANAL. 

The  CIRCULATION  of  the  liver  is  more  peculiar  and  inter- 
esting than  that  of  any  other  organ  in  the  body.  Two 
systems  bring  blood,  yet  it  leaves  through  one.  In  other 
organs,  the  vessel  that  supplies  the  functionating  tissue  is 
an  ARTERY,  but  here  it  is  a  VEIN,  the  PORTAL  VEIN. 

*Jour.  of  Anat,  Vol.  V,  No.  3. 


PORTAL    CIRCULATION.  151 

The  PORTAL  VEIN  is  made  up  of  the  superior  and  inferior 
mesenteries,  coronary  (stomach)  and  splenic  veins.  It  enters 
at  the  portal  or  transverse  fissure  of  the  liver,  and  forms 
two  main  branches,  RIGHT  and  LEFT,  one  for  each  main 
lobe.  These  rapidly  form  INTERLOBULAR  BRANCHES  that 
give  rise  to  the  INTRALOBULAR  CAPILLARIES,  found  in  the 
lobules,  where  they  converge  at  the  center  and  empty  into 

the  CENTRAL,    OK  INTRALOBULAR   VEIN. 

The  circulation  of  the  liver  might  be  outlined  as  follows: 


PORTAL  VEIN. 

I 

LOBAR  BRANCHES. 

I 

INTERLOBULAR  VEINS. 


*0sf 


Hepatic  artery. 

i 

Lobar  branches. 

i 

Interlobular  arteries. 

j 

Interlobular  capillaries. 


\  *° 

INTRALOBULAR  CAPILLARIES 


Central  vein. 

i 

Sublobular  vein. 

j 

Interlobular  vein. 

i 

Hepatic  \eins. 


152  THE    DIGESTIVE    GLANDS. 

The  HEPATIC  ARTERY  enters  the  transverse  fissure,  and 
forms  LOBAR  and  INTERLOBULAR  branches.  The  latter 
rapidly  form  capillaries  that  lie  in  the  interlobular  connective 
tissue  and  nourish  it,  and  the  vessels  found  here.  These  are 
the  INTERLOBULAR  CAPILLARIES,  some  of  which  enter  the 
outer  third  of  the  lobule  and  empty  into  the  portal  vein 
capillaries.  The  remainder  of  the  hepatic  artery  capillaries 
empty  into  the  interlobular  branch  of  the  portal  vein,  or 
form  small  venules  that  ultimately  empty  into  these. 

The  blood  that  has  entered  the  CENTRAL  VEIN,  from  the 
portal  vein  and  the  hepatic  artery,  passes  into  the  SUBLOBU- 
LAR  VEINS,  which  are  formed  by  a  union  of  the  centrals, 
and  then  into  the  INTERLOBULAR  branches  of  the  hepatic 
veins.  The  INTERLOBULARS  are  formed  by  a  union  of  the 
SUBLOBULARS,  and  these,  in  turn,  unite  to  form  the  HEPATIC 
VEINS  that  empty  the  blood  into  the  postcava,  or  inferior 
vena  cava. 

As  the  portal  vein  blood  comes  into  intimate  relation 
with  the  hepatic  cells,  the  latter  remove  the  products  re- 
quired for  nutrition,  also  the  excess  of  glucose,  which  is 
converted  into  liver  sugar,  or  glycogen,  and,  in  addition, 
take  out  the  constituents  of  the  bile;  it  is  now  considered 
the  seat  of  urea  formation. 

The  lymphatics  are  superficial  and  deep.  The  superficial 
drain  into  either  the  celiac  and  hepatic  lymph  nodes 
on  the  one  hand,  or  through  the  diaphragm  into  the  ventral 
mediastinal  nodes.  The  deep  pass  out  either  through  the 
portal  fissure  to  hepatic  and  celiac  nodes,  or  along  the  hepatic 
vein  pass  through  diaphragm  to  nodes  around  the  postcava. 

The  blood-vessels  are  surrounded  by  lymph  spaces  that 
communicate  with  the  capillaries  and  with  similar  spaces 
in  the  periphery  of  the  lobule,  and  in  the  interlobular  con- 
nective tissue. 

The  sympathetic  nerves  form  the  chief  source  of  enerva- 


SALIVARY    GLANDS.  153 

tion  of  the  liver.  They  lie  in  the  interlobular  connective 
tissue  as  plexuses,  and  from  these  some  fibres  pass  to  the 
bile  ducts,  and  others  penetrate  the  lobules  to  pass  beneath 
the  cells. 

The  Excretory  Apparatus  consists  of  the  Gall-bladder, 
Hepatic,  Cystic  and  Common  Ducts.  They  all  possess  three 
coats,  MUCOUS,  MUSCULAR  and  FIBROUS. 

In  the  Gall-bladder,  the  MUCOUS  COAT  consists  of  simple 
columnar  cells,  basement  membrane  and  tunica  propria;  the 
latter  is  thrown  into  folds,  in  which  the  muscular  coat  also 
is  included.  In  this  layer,  a  few  mucous  glands  may  be 
found,  diffuse  lymphoid  tissue  is  usually  abundant,  and 
solitary  follicles  are  not  infrequently  found. 

The  MUSCULAR  coat  consists  of  a  mixture  of  smooth 
muscle  and  white  fibrous  tissue,  the  latter  predominating 
near  the  mucous  coat.  In  the  fibrous  tissue  are  found  the 
chief  vessels  that  supply  the  other  coats  with  branches. 

The  fibrous  coat  consists  of  white  fibrous  tissue,  covered 
in  part  by  the  peritoneum. 

The  lymphatics  are  connected  to  those  of  the  liver  by  the 
subserous  plexus,  into  which  the  vessels  from  the  muscular 
coat  empty. 

The  nerves  are  sympathetic  and  cerebro spinal,  the 
former  passing  to  the  blood-vessels  and  muscles,  and  the 
latter  ending  in  the  mucosa,  near  large  arteries. 

The  Ducts  have  somewhat  the  same  structure,  containing 
a  few  mucous  glands  in  the  mucosa.  The  muscle  fibres 
are  quite  distinct.  They  are  arranged  as  circular,  longitu- 
dinal and  oblique  layers.  The  circular  fibres  of  the  common 
duct  form  a  sphincter  at  its  entrance  into  the  duodenum. 

SALIVARY  GLANDS. 

The  Salivary  Glands  are  the  Parotid,  Pancreas  (the  ab- 
dominal salivary  gland),  Sublingual  and  Submaxillary 


154  THE    DIGKSTIYi;    GLANDS. 

glands.  In  addition,  there  are  a  large  number  of  small 
unnamed  glands  in  the  lips,  mouth,  tongue,  pharynx,  base 
of  the  epiglottis,  and  esophagus. 

According  to  SECRETION,  they  are  divided  into  MUCOUS, 
SEROUS  and  MIXED. 

The  MUCOUS  glands  are  distinguished  by  their  large 
secretory  units  that  stain  lightly.  These  are  the  acini, 
alveoli  or  tubules,  and  they  give  rise  to  a  thick  viscid  secre- 
tion. Such  glands  are  the  small  glands  of  the  mouth, 
pharynx  and  esophagus.  The  SUBLINGUAL  is  almost  a 
pure  mucous  gland. 

SEROUS  glands  are  those  in  which  the  acini  stain  darkly, 
owing  to  the  presence  of  secretory  granules  in  the  protoplasm, 
which  retain  the  stain.  These  glands  secrete  a  thin  al- 
buminous fluid.  Such  are  the  PAROTID  and  PANCREAS. 

The  MIXED  glands  are  those  that  stain  both  lightly  and 
darkly,  and  secrete  a  mixed  fluid,  as  the  SUBMAXILLARY 
and  SUBLINGUAL. 

As  all  of  these  glands  have  the  same  general  structure, 
this  will  be  first  considered,  and  the  special  points  then 
noted. 

Each  is  surrounded  by  a  CAPSULE  of  white  fibrous  tissue 
that  limits  it  from  the  surrounding  organs  or  tissues.  The 
CAPSULE  sends  in  prolongations  that  divide  the  gland  into 
LOBES  and  LOBULES.  The  LOBULES,  or  STRUCTURAL  UNITS, 
consist  of  the  functionating  units  that  are  composed  of  a 
single  layer  of  glandular  epithelial  cells,  supported  by  a 
basement  membrane.  External  to  the  basement  membrane, 
is  the  interstitial,  or  intertubular  connective  tissue,  which 
is  composed  of  reticulum,  and  in  which  the  blood-vessels, 
nerves  and  lymphatics  are  found.  It  corresponds  to  the 
tunica  propria  of  a  mucous  membrane. 

The  SECRETORY  UNITS  lead  into  minute  INTERMEDIATE, 
or  INTERCALATED  TUBULES  that  unite  to  form  INTRALOBU- 


PAROTID  AND  PANCREAS.  155 

LAR  DUCTS,  which  pass  into  the  interlobular  connective 
tissue.  Here  they  unite  to  form  the  INTERLOBULAR  DUCTS; 
these,  by  union,  form  the  lobars,  and  then  the  SINGLE  EX- 
CRETORY DUCT.  The  INTERMEDIATE  TUBULES  are  lined  by 
simple  squamous  or  low  columnar  cells,  supported  by  base- 
ment membrane  and  interstitial  tissue;  the  INTRALOBULAR 
branches  contain  simple  columnar s,  the  INTERLOBULARS 
and  INTERLOBARS  are  lined  by  pseudo- stratified  columnars, 
and  the  EXCRETORY  DUCT  usually  by  stratified  columnars. 
In  the  latter  the  muscle  coat  is  distinct. 

The  blood-vessels  follow  the  divisions  of  the  ducts,  and 
form  plexuses  of  capillaries  around  the  units,  and  in  close 
proximity  to  the  epithelium. 

The  nerves  pass  down  in  the  same  manner,  and,  after 
penetrating  the  basement  membrane,  end  around  the  cells. 

The  Parotid  Gland,  a  compound  alveolar  gland,  consists  of 
small,  serous  acini,  lined  by  cells  adapted  to  fit  these  alveoli. 
The  actively  secreting  cell  has  a  very  granular  protoplasm, 
but  that  of  the  resting  cell  contains  but  few  granules. 
As  the  granules  increase,  the  protoplasm  decreases,  until 
expulsion  of  the  secretion,  and  then  the  protoplasm  again 
increases.  Secretory  capillaries  exist  between  the  cells. 

This  gland  is  not  so  definitely  limited  as  the  others,  and, 
as  a  consequence,  adipose  tissue  may  be  seen  in  the  inter- 
lobular connective  tissue,  and  the  ductular  system  is  said 
to  be  more  highly  differentiated  than  in  any  other. 

The  PAROTID  DUCT  is  the  excretory  duct.  o-^  C 

The  Pancreas,  the  other  SEROUS  GLAND,  is  also  compound 
alveolar  in  structure.  It  is  also  called  the  abdominal  sali- 
vary gland.  The  ACINI  are  usually  distinct  and  sharply  out- 
lined. In  these,  occasionally,  a  small  flat  cell  is  seen  occupy- 
ing a  central  position;  this  is  a  centro-acinar  cell,  and  is 
supposed  to  be  one  of  the  cells  lining  the  intermediate 
tubules  that  extends  into  the  acini.  In  addition  to  the  acini, 


156  THE    DIGESTIVE    GLANDS. 

certain  peculiar  collections  of  lightly-staining  cells  are  seen. 
These  are  oval  or  circular  in  outline,  and  surrounded  by  a 
capsule  of  white  fibrous  tissue.  The  cells  are  divided  into 
groups,  each  of  which  seems  to  be  environed  by  a  collection 
of  capillaries.  These  are  the  pancreatic  islands,  or  areas, 
or  islands  of  Langerhans,  and  possess  no  outlet  for  the 


FIG.  55. — SECTION  OF  HUMAN  PANCREAS  SHOWING  PANCREATIC  ISLANDS. 

a.  Interlobular  connective  tissue;  b.  capillary;  c.  interlobular  duct;  d.  in- 

tralobular  duct;  c.  cells  of  acini;  /.  area  of  Langerhans. 

secretion  they  are  supposed  to  form,  which  is,  therefore, 
supposed  to  be  absorbed  by  the  blood-vessels.  Such  is  an 
internal  secretion.  These  islands  are  considered  of  pathologic 
importance  in  a  certain  form  of  glycosuria. 

The  EXCRETORY  DUCT,  the  DUCT  OF  WIRSUNG,  is  lined  by 
simple  columnar  cells. 


SUBLINGUAL    GLAND. 


157 


The  Sublingual,  a  tubule-alveolar  gland,  according  to 
some  is  purely  mucous,  and  differs  from  the  above  in  pos- 
sessing lightly-staining  cells  in  the  secretory  units.  These 
cells  are  large  and  clear  during  secretory  activity,  but 
smaller  and  cloudy  after  expulsion  of  the  contents.  The 


*&£&*  O-*          ri>~ 


>ir 


H^x 

- 


c^J; '  /vf'- 
:B^s<^-viif  !>4  :S^r-  srt 

^&&M£^: 


y 


FIG.  56. — SECTION  OF  SUBMAXILLARY  GLAND  OF  A  Fox. 

a.  Connective  tissue;  b.  serous  acinus;  c.  intralobular  ducts;  d.  lumen  of  a 

mucous  acinus;  e.  mucous  cells;  /.  demilune  of  Heidenhain;  g.  capillary. 

nucleus  is  usually  peripheral,  in  the  former  condition. 
Besides  the  above  cells,  there  are  certain  darkly-staining 
cells  or  cell-groups,  at  the  periphery  of  the  tubules,  lying 
between  the  mucous  cells  and  the  basement  membrane. 
These  are  crescent-shaped,  and  are,  therefore,  called  the 


158  nil'.   DIGKSTIYI;  GLANDS. 

cresents  of  Gianuzzi,  or  demilunes  of  Heidenhain.  Accord- 
ing to  Stohr,  they  represent  stages  of  secretory  activity,  in 
which  the  cells  have  expelled  their  secretion.  Others 
hold  them  to  be  separate  SEROUS  cells,  and  that  accounts  for 
their  dark  stain.  Secretory  canals  are  said  to  exist  in  them, 
and  this  would  seem  to  point  to  a  serous  character. 

There  are  usually  several  ducts,  called  the  SUBLINGUAL 
DUCTS  or  DUCTS  OF  RIVINUS.  If  but  one  is  present  it  is 
called  the  DUCT  OF  BARTHOLIN. 

The  Submaxillary  is  a  MIXED  gland  in  secretion,  and 
tubulo-alveolar  in  structure.  The  SEROUS  and  MUCOUS  UNITS 
may  be  separated  into  lobules  or  lobes,  or  may  be  found  side 
by  side  in  the  same  lobule.  The  serous  are  the  more  numer- 
ous in  man.  In  the  mucous  tubules,  demilunes  are  present. 
The  ducts  are  unusually  numerous,  forming  a  distinguishing 
feature  of  this  gland. 

The  excretory  duct  is  the  SUB-MAXILLARY  DUCT,  or  DUCT 
OF  WHARTON. 


CHAPTER  XI. 


RESPIRATORY  SYSTEM. 

This  System  comprises  the  Nares,  upper  part  of  the 
Pharynx,  the  Larynx,  Trachea,  Bronchi  and  Lungs.  Al- 
though there  is  no  connection,  the  Thyroid  and  Parathyroids 
are  included  in  this  Chapter. 

The  Nares  are  lined  by  a  mucous  membrane,  which  differs 
according  to  the  function  of  the  part.  The  FIRST  portion  is 
lined  by  stratified  squamous  cells,  continued  from  the  skin 
surface.  Here  are  found  some  large  hairs,  sweat  and 
sebaceous  glands.  Within  this  area,  the  TRUE  RESPIRATORY 
portion  is  lined  by  stratified  ciliated  cells,  with  a  few  goblet 
cells  scattered  here  and  there.  Beneath  the  basement 
membrane,  the  tunica  propria  is  represented  by  a  delicate 
fibrous  tissue  containing  some  diffuse  lymphoid  tissue  and 
some  glands  of  the  mucous  and  serous  types.  Above  this 
area,  the  OLFACTORY  MUCOUS  MEMBRANE  is  found. 

The  RESPIRATORY  portion  of  the  PHARYNX,  continuous 
with  the  nares,  is  lined  by  stratified  ciliated  cells.  In  the 
tunica  propria,  glands  resembling  those  found  in  the  nares 
are  seen. 

LARYNX. 

The  Larynx  is  a  hollow,  cartilaginous  organ  connecting 
the  pharynx  with  the  trachea.  It  consists  of  EPIGLOTTIS, 
VOCAL  CORDS  and  LARYNX  PROPER. 

The  EPIGLOTTIS  is  a  projecting  flap  that  protects  the 
GLOTTIS  during  deglutition.  It  is  covered  by  stratified 

159 


l6o  RKSI'IRATORY    SVSTKM. 

squamous  cells  upon  both  sides,  and  these  are  continuous 
at  the  edges,  and  rest  upon  basement  membrane  and  papil- 
lated  tunica  propria.  The  latter  is  composed  of  fibro-elastic 
tissue,  and  contains  diffuse  lymphoid  tissue,  and,  also,  some 
glands,  near  its  attachment.  In  the  epithelial  portion  of 
the  ventral  surface,  taste-buds  are  found.  Beneath  the  tun- 
ica propria  is  the  submucosa,  which  consists  of  loose  white 
fibrous  connective  tissue.  In  it  is  found  a  plate  of  elastic 
cartilage  that  gives  the  stiffness,  and  also  the  elasticity,  to 
this  organ. 

The  VOCAL  CORDS  comprise  the  TRUE  and  the  FALSE.  The 
FORMER  are  the  functionating  structures,  while  the  latter 
are  merely  heavy  folds  that  seem  to  resemble  the  former. 
The  TRUE  CORDS  alone  are  of  importance. 

The  TRUE  VOCAL  CORDS,  PLic^:  VOCALES,  are  covered  by 
stratified  squamous  cells  that  are  supported  by  basement 
membrane  and  tunica  propria.  The  central  portion  consists 
of  a  band  of  elastic  tisssue.  They  contain  no  glands. 

Between  the  two  sets  of  cords,  there  is  a  space,  or  recess, 
upon  each  side,  called  the  ventricle  of  the  larynx. 

The  remainder  of  the  larynx  consists  of  MUCOUS,  SUB- 
MUCOUS  and  FIBROUS  coats. 

The  MUCOUS  coat,  including  that  of  the  ventricles,  is  lined 
by  stratified  ciliated  epithelial  cells.  The  tunica  propria 
contains  a  great  deal  of  diffuse  lymphoid  tissue.  That  por- 
tion of  the  SUBMUCOSA  adjacent  to  the  tunica  propria 
possesses  a  number  of  small  mucous  glands.  In  its  outer 
portion,  the  cartilage  masses  are  found. 

The  form  of  the  larynx  is  given  by  the  cartilages,  which 
are  chiefly  hyalin.  Those  of  Wrisberg  and  Santoriniy  middle 
of  the  thyroid  and  the  apices  of  the  arytenoids  are  elastic 
cartilage. 

External  to  the  cartilage  is  the  fibrous  coat,  which  is  com- 
posed of  white  fibrous  tissue,  supports  the  other  coats, 


TRACHEA.  l6l 

and  connects  the  larynx  to  the  surrounding  organs  or 
tissues. 

The  blood-vessels,  nerves  and  lymphatics  are  numerous. 
The  circulatory  system  is  represented  by  several  networks 
of  large  vessels,  and  a  plexus  of  capillaries  in  the  tunica 
propria. 

The  lymphatics  closely  follow  the  blood-vessels. 

The  nerves  are  distributed  to  the  mucosa,  where  they  end 
near  and  within  the  epithelial  layer,  or  in  the  taste-buds. 

TRACHEA. 

The  Trachea  connects  the  larynx  with  the  lungs,  its  lower 
end  bifurcating  to  form  the  Bronchi.  It  has  THREE  COATS, 
MUCOUS,  SUBMUCOUS  and  FIBROUS. 

The  MUCOUS  coat  is  a  continuation  of  that  of  the  larynx. 
It  is  composed  chiefly  of  stratified  ciliated  and  goblet  cells 
that  rest  upon  the  basement  membrane  and  tunica  propria. 
The  basement  membrane  is  usually  quite  prominent,  and 
the  tunica  propria  contains  considerable  diffuse  lymphoid 
tissue.  It  consists  of  fibre-elastic  tissue,  in  which  the 
fibres  have  chiefly  a  longitudinal  direction.  That  portion 
of  the  mucosa  opposite  to  the  attachment  to  the  esophagus 
is  lined,  at  times,  by  stratified  squamous  cells,  and  is  usually 
irregular. 

The  SUBMUCOSA  is  made  up  of  white  fibrous  tissue,  and 
supports  the  large  blood-vessels  and  a  large  number  of 
mucous  glands,  the  tracheal  glands.  These  lie  in  that 
portion  near  the  tunica  propria.  In  the  outer  part  are 
found  the  cartilage  rings. 

These  so-called  rings  are  C-shaped  masses  of  hyalin  car- 
tilage, with  the  open  portion  at  the  attachment  of  the  organ 
to  the  esophagus.  These  masses  are  thickest  in  front,  and 
taper  as  the  ends  are  reached.  Although  the  cartilages  are 


162 


RESPIRATORY    SYSTI.M. 


supposed  to  consist  of  one  piece,  they  are  commonly  made 
up  of  a  number  of  plates.  The  ends  of  the  C's  are  con- 
nected by  traversely  and  longitudinally  arranged  smooth 


-,vv,»-ii  s-- 


•r^x- 


FIG.  57. — CROSS-SECTION  OF  SK<;MK.\T  OK  THK  TRACHKA. 
a.  Mucous  coat;  b.  submucous  coat;  r,  d.  fibrous  coat  containing  sonic  vol- 
untary striated  muscle,  /,  m;  e.  stratified  ciliated  epithelium;/,  basement 
membrane;  g.  goblet  cells;  h.  mucous  glands;  i.  blood-vessel;  k.  elastic- 
tissue  and  perichondrium;  /.  longitudinal,  and  ;;?,  cross-sections  of 
voluntary  muscle  fibres. 

muscle  fibres,  which  are  attached  to  the  inner  and  outer 
perichondriums,  and  then  bridge  the  spaces  between  the 
ends  of  the  cartilage.  This  strip  of  muscle  extends  the 
length  of  the  trachea,  but  no  complete  muscularis  is  present. 


LUNGS.  163 

The  rings  are  sixteen  to  eighteen  in  number,  and  are 
separated  from  one  another  by  white  fibrous  tissue. 

The  FIBROUS  coat  lies  outside  of  the  cartilage  rings,  and 
consists  of  white  fibrous  and  yellow  elastic  tissues. 

The  blood-vessels  and  lymphatics  have  their  larger 
branches  in  the  submucosa,  from  which  smaller  vessels  ex- 
tend to  the  other  coats,  and  form  capillaries. 

The  nerves  are  chiefly  sympathetic. 

The  Bronchi  have  the  same  general  structure  as  the 
trachea.  Usually  the  C-shaped  ring  of  cartilage  is  re- 
placed by  a  number  of  plates. 

LUNGS. 

The  Lungs  resemble  compound  racemose  glands,  the 
BRONCHI  corresponding  to  the  excretory  ducts. 

Each  Lung  is  invested  by  &  fibrous  sheath,  covered  almost 
entirely  by  serous  membrane,  the  VISCERAL  LAYER  OF  THE 
PLEURA,  which  is  reflected  over  the  inside  of  the  pleural 
cavity,  as  the  parietal  layer  of  the  pleura.  Between  these 
two  layers  is  the  so-called  pleural  cavity,  but  as  the  lungs 
fill  it  in  the  living  condition,  it  does  not  exist  as  a  cavity. 
In  it  is  found  a  small  amount  of  lymph  that  lubricates  the 
membranes. 

The  Pleurae  have  the  same  structure  as  other  serous 
membranes.  Each  consists  of  endothelial  cells  and  subendo- 
thelial  connective  tissue  that  pass  from  the  lung  over  to  the 
body  wall.  The  sub  endothelial  tissue  is  continuous  with  the 
interlobular  connective  tissue  of  the  lung. 

Upon  the  internal  surface  of  the  lung  is  an  area,  in  which 
the  vessels  and  tubes  enter  and  leave  the  organ;  this  is  the 
ROOT  of  the  lung,  and  here  no  serous  membrane  exists. 

The  LUNGS,  like  other  glands,  are  merely  systems  of  tu- 
bules that  branch  and  rebranch,  and  are  lined  by  different 


1 64 


RESPIRATORY    SYSTEM. 


varieties  of  cells.  Each  is  an  aheolo-tubular  gland,  and  al- 
though no  liquid  secretion  or  excretion  is  formed,  it  plays 
an  important  part  in  the  excretion  of  gases  and  organic 
matter  from  the  blood  and  in  the  oxygenation  of  the  blood. 
The  Bronchi  divide  like  the  ducts  of  any  gland,  and, 


FIG.  58. — SECTION  OF  HUMAN  LUNG. 

a.  Pleura;  b.  alveolar  septum;  c.  alveus,  or  air  sac;  d.  alveolus;  e.  intralobular 
blood-vessel;  /.  interlobular  blood-vessel;  g.  interlobular  bronchial 
tube;  h.  cartilage;  i.  branch  of  pulmonary  artery;  k.  gland. 

ultimately,  the  small  divisions  called  BRONCHIOLES  are 
reached.  Each  BRONCHIOLE  forms  a  system  separate  and 
closed  from  its  neighbors.  The  BRONCHIOLE  (0.5  mm.  in 
diameter)  divides  into  the  RESPIRATORY  BRONCHIOLES 
(0.3  to  0.4  mm.  in  diameter);  these,  in  turn,  give  rise  to 


LUNGS.  165 

ALVEOLAR  DUCTS  (0.2  mm.),  which  end  as  large  spaces, 
the  ALVEI,  ALVEOLAR  SACS  or  AIR  SACS  (0.3  by  5  mm.); 
along  the  walls  of  these  divisions,  are  found  small  depressions 
the  ALVEOLI,  or  SACCULES  (0.05  to  o.i  mm.),  and  these  are 
the  final  divisions. 

A  LOBULE,  or  STRUCTURAL  UNIT,  consists  of  the  divisions 
of  a  bronchiole,  and  varies  from  0.3  cm.  to  3  cm.  in  diameter. 
It  is  surrounded  by  white  fibrous  tissue  containing  larger 
vessels  and  ducts,  which  are  called  interlobular,  are  over 
0.5  mm.  in  diameter,  and  contain  cartilage.  The  alvei, 
or  air  sacs,  are  separated  from  one  another  by  yellow  elastic 
tissue,  in  which  a  dense  capillary  plexus  is  found. 

As  the  BRONCHUS  divides  and  redivides,  the  tubules  con- 
tain less  and  less  cartilage.  The  first  important  change  is 
the  formation  of  a  complete  investment  of  cartilage,  com- 
posed of  a  number  of  plates.  As  this  occurs,  the  muscle 
tissue  begins  to  increase,  so  that  soon  a  distinct  layer  is  seen 
internal  to  the  cartilage.  The  lining  cells  are  stratified  cili- 
ated, but  the  whole  mucosa  becomes  irregular  and  corru- 
gated, due  to  the  formation  of  longitudinal  folds;  as  the 
divisions  become  smaller,  the  cartilage  diminishes.  The 
glands  disappear  when  a  diameter  of  i  mm.  is  reached. 
The  cartilage  is  retained  until  a  diameter  of  0.5  mm.  is 
attained. 

Such  a  tubule  is  a  BRONCHIOLE.  It  is  lined  by  simple 
ciliated  epithelial  and  goblet  cells,  supported  by  a  basement 
membrane  and  an  elastic  tunica  propria.  External  to  this, 
the  circular  muscle  fibres  are  quite  prominent,  and  as  a  re- 
sult, folds  are  formed.  The  fibrous  tissue  external  contains 
elastic  fibres,  as  well  as  vessels  and  nerves. 

The  RESPIRATORY  BRONCHIOLES  arise  by  a  division  of  the 
above  tubules.  They  are  lined  partially  by  simple  ciliated 
and  partially  by  nonciliated  cells.  The  former  are  of  the 
simple  variety,  and  few  in  number.  The  nonciliated  cells 


l66  RESPIRATORY    SYSTEM. 

at  first  are  columnar,  but  quickly  give  way  to  low  cuboidal 
and  flattened  cells.  The  last  named  are  called  respiratory 
epithelium.  Along  the  walls  of  the  tubules,  little  depres- 
sions, the  alveoli,  are  seen,  and  here  the  respiratory  epithe- 
lium is  marked.  Muscle  fibres  are  found  beyond  the 
tunica  propia,  and  elastic  tissue  becomes  more  abundant. 

The  ALVEOLAR  DUCTS  contain  many  alveoli  lined  by 
respiratory  epithelium,  which  consists  of  thin,  nonnucleated 
plates  of  various  sizes,  arranged  individually  or  in  groups. 
The  smaller  cells  are  derived  from  the  cuboidal  cells  and 
are  flattened  by  inspiration,  and  the  larger  are  formed  by 
a  fusion  of  the  smaller  ones.  The  walls  of  these  ducts 
consist  of  tunica  propria,  muscle  tissue  (which  disappears 
when  the  end  of  this  tubule  is  reached)  and  considerable 
elastic  tissue  circularly  arranged. 

The  alveolar  ducts  lead  into  the  ALVEUS,  AIR  SAC,  or  ALVE- 
OLAR SAC.  On  the  walls  of  this  part  are  the  small  depres- 
sions, the  ALVEOLI  or  SACCULES.  These  are  separated 
from  one  another  by  minute  partitions,  or  septa,  that 
consist  of  elastic  tissue  covered  by  simple  squamous  cells, 
the  respiratory  epithelium.  The  ALVEOLI  of  a  system  com- 
municate with  one  another  by  means  of  small  channels,  or 
pores.  At  the  base  of  the  alveolus,  the  elastic  tissue  is 
formed  into  a  thick  ring.  In  the  meshwork  of  the  elastica 
of  an  alveolus  is  found  a  dense  plexus  of  blood-capillaries. 
The  amount  of  elastica  allows  a  great  increase  in  size  of 
the  air  sacs  (2  to  3  times). 

From  W.  S.  Miller's  careful  studies  on  the  structure  of 
the  lungs,  the  terminal  bronchioles  terminate  as  follows: 
Each  respiratory  bronchiole  divides  into  one  or  more  alve- 
olar ducts,  which  widen  at  their  outer  ends.  Each  duct 
opens  into  several  vestibula;  from  each  vestibulum,  a  num- 
ber of  atria  open,  which,  in  turn,  communicate  with  the 
air  sacs,  or  alvei,  on  the  walls  of  which  are  the  alveoli. 


LUNGS.  167 

The  circulatory  system  is  peculiar.  As  in  the  liver,  two 
sets  of  vessels  enter,  the  pulmonary  and  bronchial,  but,  un- 
like those  of  the  liver,  they  do  not  unite  to  form  a  single 
system,  but  remain  individual.  There  is  some  anastomosis 
between  the  two  systems  of  vessels. 

The  pulmonary  artery  conveys  the  blood  to  be  oxygenated 
and  is  the  nutrient  vessel  of  the  functionating  epithelial 
cells.  It  branches  at  the  root,  and  the  divisions  follow 
those  of  the  bronchus  very  closely.  Between  the  lobules, 
its  branches  are  the  interlobular  divisions,  and  these  penetrate 
the  lobules  to  form  the  densest  capillary  plexus  of  the  body, 
within  the  elastica  of  the  alveoli.  Here  the  endothelial 
cells  of  the  capillary,  and  the  squamous  epithelial  cell  of  the 
alveolus,  separate  the  blood  from  the  air.  Such  an  exceed- 
ingly thin  membrane  allows  the  interchange  of  oxygen 
and  effete  gases,  and  also  the  absorption  of  nutrient  matter 
by  the  epithelial  cells,  and  the  outward  passage  of  the 
waste  matter.  The  blood  is  collected  by  the  venous  radicals 
of  the  pulmonary  vein,  and  these  unite  to  form  the  inter- 
lobular branches,  that  ultimately  form  the  pulmonary  veins. 

The  bronchial  artery  branches  somewhat  as  the  pulmonary 
artery,  but  its  divisions  do  not  penetrate  to  the  same  degree. 
They  enter  the  lobule  and  form  capillaries  around  the  vessels 
and  ducts  here  and  nourish  them,  but  not  the  respiratory 
epithelium.  The  capillaries  lie  in  the  interlobular  connect- 
ive tissue,  and  supply  the  vessels  there  with  nutrient 
material.  Between  these  two  sets  of  vessels,  the  pulmonary 
and  bronchial  arteries,  there  is  some  anastomosis,  so  that 
the  pulmonary  veins  carry  some  of  the  bronchial  artery 
blood  from  the  lungs.  The  bulk  of  the  bronchial  blood, 
however,  is  collected  by  the  divisions  of  the  bronchial  veins 
that  finally  empty  into  the  vena  azygos,  right  and  left  (or 
left  superior  intercostal). 

The  lymphatics  are  superficial  and  deep;  the  former  lie 


l68  RESPIRATORY    SYSTEM. 

beneath  the  pleurae  and  connect  with  the  deep  plexus. 
The  latter  consists  of  vessels  that  follow  the  blood-vessels 
and  lie  in  the  interlobular  connective  tissue;  these  have  a 
number  of  bronchial  lymph  nodes  (incorrectly  called  bron- 
chial glands)  in  their  course. 

The  nerves  are  mainly  sympathetic,  though  the  vagus 
sends  branches  to  the  lungs.  They  end  chiefly  in  the  blood- 
vessels. 

The  following  are  the  epithelial  cells  that  line  the  various 
portions  of  the  Respiratory  Tract: 

^.  f  FIRST  PART       ....  Stratified  squamous. 

\  SECOND  PART   ....  Stratified  ciliated. 

PHARYNX Stratified  ciliated. 

f  EPIGLOTTIS     ....  Stratified  squamous. 
LARYNX  -j  VOCAL  CORDS      .      .    .  Stratified  squamous. 
(  REMAINDER  OF  LARYNxStratified  ciliated. 

TRACHEA Stratified  ciliated. 

BRONCHI Stratified  ciliated. 

BRONCHIAL  TUBES Stratified  ciliated. 

(  Simple  ciliated. 

BRONCHIOLES •    i  Simple  columnar. 

[  Simple  squamous  (respiratory). 

ALVEOLAR  DUCTS       Simple  squamous  (respiratory). 

ALVEOLI       Simple  squamous  (respiratory). 

THYROID  BODY. 

The  Thyroid  Body  is  a  ductless,  compound  tubular  gland, 
and  consists  of  two  large  lateral  lobes  united  by  a  narrow 
band,  the  middle  lobe,  or  isthmus. 

The  organ  is  surrounded  by  a  capsule  that  sends  in  trabec- 
ulae,  which  divide  the  gland  into  lobes  and  lobules.  These 
divisions  are  irregular,  and  the  lobules  are  composed  of  a 
number  of  short  tubules,  sometimes  called  follicles.  Each 
tubule  is  lined  by  cuboidal  epithelial  cells  that  rest  upon  a 
basement  membrane;  outside  of  this  is  the  intralobular,  or  in- 


THYROID    BODY.  169 

/( 'r tubular ,  connective  tissue  that  supports  the  blood-vessels. 
In  the  tubules  is  seen  a  peculiar,  homogeneous  substance, 
the  colloid  substance,  that  is  supposedly  the  result  of  the 
activity  of  the  cells.  It  has  a  yellowish  color,  and  as  blood- 
cells  are  frequently  seen  in  it,  the  color  may  be  due  to  the 
hemoglobin  from  these.  Sometimes,  the  colloidal  material 
is  shrunken,  and  then  its  edges  are  crenated;  in  such  tubules, 


FIG.  59. — SECTION  OF  HUMAN  THYROID  GLAND. 

a.  Epithelium;  b.  basement  membrane;  c.  colloid  substance;  d.  interlobular 
connective  tissue;  e.  interlobular  vein. 


the  epithelial  cells  are  drawn  away  from  the  basement 
membrane.  Gulland  and  Goodall  found  granules  of  iron 
in  the  interlobular  tissue  cells  and  in  the  epithelial  cells  of 
the  tubules.  These  granules  were  most  abundant  in  those 
tubules  in  which  the  colloid  substance  was  small  in  amount. 
It  is  not  unusually  found  that  the  colloid  substance  in  the 
same  tubule  is  of  different  reaction,  most  of  it  responding 
to  protoplasmic  stains,  while  a  smaller  amount,  centrally 


170  RESPIRATORY    SYSTCM. 

located  and  surrounded  by  the  preceding,  responds  to 
the  nuclear  stain. 

Blood-vessels  are  numerous,  and  dense  plexuses  are 
formed  around  the  tubules.  It  is  thought  that  the  colloid 
material  may  represent  an  internal  secretion  that  is  absorbed 
by  the  blood-vessels,  or  perhaps  the  lymphatics. 

The  lymphatics  are  numerous,  and  lie  between  the 
tubules.  They  often  contain  some  of  the  colloid  substance. 

PARATHYROIDS. 

The  Parathyroids  are  usually  four  in  number,  two  of 
which  lie  in  close  relation  with  each  lateral  lobe  of  the 
THYROID.  They  are  small,  and  the  epithelial  cells  are 
usually  of  the  glandular  type,  and  are  arranged  in  groups,  or 
chains,  forming  a  network,  or  even  tubules.  These  cells 
respond  very  readily  to  the  protoplasmic  stains  and  are 
usually  quite  deeply  stained,  in  marked  contrast  to  the 
cells  of  the  thyroid  body.  Between  the  cells  is  white 
fibrous  connective  tissue  that  supports  quite  a  capillary 
plexus.  Occasionally,  colloid  material  is  seen  in  the  tubules. 
When  the  thyroids  are  removed  and  the  parathyroids 
remain,  they  hypertrophy  and  carry  on  the  function  of  the 
removed  organs.  According  to  some  investigators,  the 
parathyroids  do  not  assume  the  function  of  the  thyroids. 
Removal  of  the  parathyroids  is  fatal  within  a  short  time. 


CHAPTER  XII. 


THE  URINARY  SYSTEM. 

The  Urinary  Organs  comprise  the  Kidneys,  Ureters, 
Bladder  and  Urethra.  On  account  of  its  proximity  to  the 
kidney,  the  Adrenal  will  also  be  considered. 

The  Kidney  is  a  compound  tubular  gland,  and,  next  to 
the  liver,  the  largest  in  the  body.  It  lies  in  a  mass  of 
adipose  tissue,  the  perirenal  fat,  from  which  it  is  readily 
separated.  Some  of  this  fat  persists  even  when  the  animal 
dies  of  starvation. 

The  kidney  is  surrounded  by  a  thin  CAPSULE  of  white 
fibrous  tissue  that  normally  strips  readily  from  the  organ. 
This  is  of  great  importance,  when  the  organ  is  studied 
pathologically.  Beneath  the  capsule  is  the  kidney  PAREN- 
CHYMA that  consists  of  a  great  number  of  tubules,  the 
uriniferous  tubules,  that  have  a  very  irregular  course. 
Along  the  internal  margin  is  a  depression  or  notch,  the 
HILUS,  at  which  the  vessels  enter  and  leave. 

When  the  organ  is  sectioned,  upon  microscopic  examina- 
tion it  is  seen  to  consist  of  an  outer  margin,  the  cortex,  and 
an  inner  broader  portion,  the  medulla.  Just  within  the  hilus 
is  seen  a  space,  the  SINUS,  containing  the  PELVIS  and  the 
main  branches  of  the  renal  artery  and  vein. 

The  cortex  constitutes  the  outer  third  of  the  organ,  and 
is  further  subdivided  into  MEDULLARY  RAYS  and  LABYRINTH. 
This  division  is  represented  by  the  alternating  dark  and 
light  bands,  which  are  at  right  angles  to  the  capsule,  and 
gives  a  striated  appearance  to  the  cortex. 


172 


THE    URINARY    SYSTK.M. 


The  MEDULLARY  RAYS,  or   PYRAMIDS  OF  FERREIN,  Consist, 

microscopically,  of  the  straight  portions  of  the  tubules  that 


FIG.  60. — SECTION  OF  HUMAN  KIDNEY  SHOWING  CORTEX  AND  MEDULLA. 

a.  Capsule;  b.  cortex;  c.  medulla;  d.  labyrinth;  e.  medullary  ray;/,  renal 
bodies;  g.  area  in  which  renal  body  has  dropped  out;  h.  capsule 
of  Bowman;  i.  glomerulus;  k.  afferent  arteriole;  /.  neck  of  uriniferous 
tubule;  m.  tubules  of  labyrinth;  n.  longitudinal  sections  of  collecting 
tubules;  o.  cross-sections  of  collecting  tubules. 

extend  from  the  medulla  into  the  cortex,  surrounded  by  the 
intertubular,  or  interstitial  reticulum.     They  never  extend 


KIDNEY.  173 

to  the  capsule,  but  diminish  in  width  as  the  outer  portion 
of  the  cortex  is  approached. 

The  LABYRINTH  lies  between  the  medullary  rays,  and  is 
composed  of  the  MALPIGHIAN,  or  RENAL,  CORPUSCLES,  the 
starting  points  of  the  tubules,  and  the  convoluted  portions  of 
the  uriniferous  tubules.  These  are  supported  by  the 
interstitial  connective  tissue  that  contains  the  blood-vessels. 

The  RENAL  CORPUSCLES  are  found  only  in  the  cortex, 
and  here  are  limited  to  the  labyrinth.  Each  one  consists 
of  a  tuft  of  arterial  capillaries,  the  GLOMERULUS,  or  RENAL 
TUFT,  surrounded  immediately  by  a  delicate  double  mem- 
brane of  simple  squamous  cells,  resting  upon  a  basement 
membrane.  The  inner  layer  lies  upon  the  tuft,  and  the 
outer  forms  the  wall  of  the  tubule.  This  membrane  is 
BOWMAN'S  CAPSULE,  and,  with  the  tuft,  comprises  the 
RENAL  CORPUSCLE.  The  tuf t  itself  is  not  a  simple  structure. 
The  arteriole,  upon  entering,  divides  into  a  number  of 
branches,  each  of  which  forms  a  set  of  capillaries.  This 
apparent  lobulation  is  quite  distinct.  As  these  capillaries 
unite  to  form  an  efferent  arteriole,  this  arrangement  is 
called  a  retia  mirabilia. 

The  medulla  is  sharply  outlined  from  the  cortex,  micro- 
scopically, by  the  absence  of  renal  corpuscles  and  the 
regularity  of  the  tubules.  At  the  junction  are  to  be  found 
the  great  vessels,  and  this  portion  is  called  the  boundary 
zone.  The  medulla  consists  of  the  MEDULLARY,  or  MAL- 
PIGHIAN PYRAMIDS,  separated  from  one  another  by  the 
COLUMNS  of  BERTIN. 

The  MEDULLARY  PYRAMIDS  are  ten  to  sixteen  in  number. 
Their  bases  continue  with  the  cortex,  and  their  apices  are 
directed  toward  the  hilus  and  project  into  the  sinus.  Each 
consists  of  a  large  number  of  straight  tubules  that  become 
fewer  in  number  as  the  apex  is  reached,  where  but  fifteen 
to  twenty  are  present.  These  are  the  PAPILLARY  DUCTS, 


174  THE    URINARY    SYSTKM. 

OR   DUCTS   OF    BELLINI.     The    tubules   are   supported    by 
reticulum,  in  which  the  capillaries  are  found. 

The  PYRAMIDS  are  separated  from  one  another  by  a 
narrow  band  of  tissue,  that,  near  the  apices,  is  chieily 
white  fibrous;  toward  the  bases,  the  parenchyma  begins 
to  enter  into  its  formation.  This  is  the  column  of  Berlin, 
and  within  it  are  the  large  vessels  that  pass  from  the  sinus 
to  the  boundary  zone. 

The  PYRAMIDS  represent  the  embryonal  condition  when 
the  whole  organ  consisted  of  lobes.  At  birth,  usually, 
the  bases  of  the  lobes  have  fused  to  form  the  cortex,  but 
the  inner  ends  never  reach  that  condition.  The  columns  of 
Berlin  then  represent  the  interlobar  connective  tissue  and 
spaces.  In  some  animals  the  lobulation  never  disappears. 

The  uriniferous  tubule  has  a  very  peculiar  and  convoluted 
course.  It  starts  in  the  cortex,  and  passes  into  the  medulla, 
to  return  to  the  cortex  for  its  final  passage  through  the 
medulla.  It  originates  at  the  RENAL  CORPUSCLE,  which 
is  merely  the  invaginated  end  of  the  tubule,  containing  a 
tuft  of  capillaries.  From  this,  the  presence  of  a  double 
capsule  can  be  readily  understood.  The  corpuscle  is 
succeeded  by  a  narrow  constricted  portion,  the  NECK, 
lined  by  simple  squamous  cells  lying  upon  a  basement 
membrane,  and  supported  by  interstitial  connective  tissue, 
which  continues  throughout.  The  next  portion,  the  PROXI- 
MAL, OR  FIRST  CONVOLUTED  tubule,  as  its  name  indicates, 
is  very  convoluted  and  irregular.  This  part  lies  in  the 
labyrinth,  and  is  lined  by  cuboidal  cells,  in  which  the 
protopasm  is  granular  and  the  cell  boundaries  are  indistinct. 
That  part  of  the  cell  near  the  lumen  is  striated.  This 
continues  as  the  DESCENDING  LIMB  of  HENLE'S  LOOP, 
which  passes  into  the  medulla  and  is  succeeded  by  the 
LOOP  and  the  ASCENDING  LIMB.  The  descending  limb  and 
the  loop,  at  times,  are  lined  by  simple  squamous  cells, 


KIDNEY.  175 

which  are  so  flat  that  the  nuclei  project.  The  ascending 
limb,  and,  according  to  some,  the  loop,  contains  simple 
cuboidal  cells,  which  may  begin  as  flat  cells.  The  proto- 
plasm of  these  is  striated.  The  continuation  of  the  ascend- 
ing is  the  SECOND,  or  DISTAL,  CONVOLUTED  tubule,  and  here 
the  cells  are  cuboidal  and  irregular,  and  the  protoplasm 
granular  and  striated.  This  portion  lies  in  the  labyrinth, 
and  is  succeeded  by  a  short,  curved  portion,  the  ARCHED 
CONNECTING  tubule,  that  connects  the  irregular  with  the 
STRAIGHT  COLLECTING  tubule.  These  are  lined  by  simple 
columnar  cells  that  become  longer  as  the  papillae  are 
approached.  The  protoplasm  of  these  is  clear,  and  not 
striated.  The  STRAIGHT  TUBULES,  as  these  approach  the 
apex  of  the  pyramid,  unite  to  form  fifteen  to  eighteen  large 
excretory  tubules,  the  DUCTS  OF  BELLINI,  or  PAPILLARY 
DUCTS.  These  are  lined  by  long  columnar  cells. 

The  various  portions  of  the  URINIFEROUS  TUBULE  are 
distributed  as  follows: 

Cortex.  In  the  LABYRINTH  are  found  the  renal  corpus- 
cles, neck,  first  and  second  convoluted  tubules.  In  the 
MEDULLARY  RAYS,  the  upper  ends  of  the  descending  and 
ascending  limbs  of  Henle's  loop  and  straight  collecting  tubules, 
and  the  arched  connecting  tubule. 

Medulla.  The  lower  ends  of  the  descending  and  ascend- 
ing limbs  and  the  loop  of  Henle  and  the  straight  collecting 
tubules  and  papillary  ducts. 

The  diameter  of  the  different  parts  of  the  tubule  varies. 
The  RENAL  CORPUSCLE  is  large,  measuring  120  to  200 
microns.  The  NECK  averages  about  15  microns,  and  the 
PROXIMAL  CONVOLUTED  TUBULE  is  quite  irregular,  but  the 
average  is  about  40  microns.  The  DESCENDING  LIMB  is 
quite  narrow,  10  to  13  microns,  and  the  ASCENDING  LIMB 
about  25.  In  the  SECOND  CONVOLUTED  TUBULE,  the 
diameter  again  increases,  averaging  40  to  45  microns. 


i76 


Till;    URINARY    SYSTEM. 


From  the  beginning  of  the  STRAIGHT  TUBULE  to  the  end, 
the  diameter  progressively  increases,  so  that  the  PAPILLARY 
DUCTS  may  have  a  diameter  of  200  microns. 

The  blood-vessels  have  a  characteristic  distribution.  The 
RENAL  ARTERY  passes  through  the  HILUS  and  enters  the 
SINUS,  where  it  divides  into  a  number  of  branches,  of 


-  5 


FIG.  61. — SECTION  OF  INJECTED  KIDNEY  OF  GUINEA-PIG. 
i.  Interlobular   (cortical)   artery;    2.   afferent   vessel;   3.   efferent   vessel;    4. 
capillary  network  in  medullary  ray;  5.  capillary  network  in  labyrinth;  6. 
interlobular  (cortical)  vein  (Stbhr's  Histology). 

which  the  greater  number  supply  the  ventral  pyramids,  and 
the  ventral  portions  of  the  dorsal  pyramids.  The  branches 
that  go  to  the  ventral  pyramids  carry  the  greater  part  of  this 
blood.  The  rest  of  the  kidney  is  supplied  by  the  dorsal 
branches.  The  branch  that  supplies  each  pole,  derived 


KIDNEY.  177 

from  the  ventral  division,  divides  into  ventral,  middle  and 
dorsal  branches,  which  are  in  no  way  united.  The  trunks 
pass  up  through  the  columns  of  Berlin,  where  small  branches 
are  given  off  to  the  vessels  and  tissues,  as  the  INTERLOBAR 
BRANCHES.  These  branches  pass  to  the  boundary  zone, 
where  they  arch  between  the  cortex  and  medulla,  form- 
ing the  ARTERIAL  ARCHES,  or  ARCADE.  From  the  cortical 
side  of  the  arch,  the  CORTICAL,  or  INTERLOBULAR,  arteries 
are  sent  toward  the  capsule;  from  these,  small  arterioles, 
AFFERENT,  pass  to  the  RENAL  corpuscles,  enter  and  form 
several  smaller  branches,  each  of  which  breaks  into  a 
capillary  tuft.  From  this,  it  will  be  seen  that  the  renal 
tuft  consists  of  several  bunches  of  capillaries.  Each 
capillary  group  is  separate,  and  the  vessels  unite  to  form 
arterioles  that  leave  the  tuft  as  a  single  vessel,  the  EFFERENT 
arteriole.  The  blood  is  still  arterial.  The  EFFERENT  arteri- 
oles soon  form  DENSE  PLEXUSES  OF  CAPILLARIES  around 
the  tubules  of  the  labyrinth  and  medullary  rays.  Those 
capillaries  near  the  boundary  zone  pass  into  the  medulla 
and  surround  the  tubules  there.  The  CAPILLARIES  become 
VENOUS  in  character,  and  unite  with  others  to  form  the 

INTERLOBULAR    VEINS.       The     CORTICAL     ARTERY    continues 

to  the  capsule,  where  it  forms  a  star-shaped  mass  of 
venules,  the  VEN/E  STELLATE.  These  are,  in  reality,  the 
starting-points  of  the  INTERLOBULAR  VEINS,  which  run 
parallel  to  the  arteries  of  the  same  name,  and  empty  into 
a  VENOUS  ARCADE  that  is  formed  at  the  boundary  zone 
by  the  union  of  the  large  vessels.  Such  is  the  blood 
supply  of  the  CORTEX. 

The  MEDULLA  receives  its  blood  from  the  concave  surface 
of  the  arterial  arch.  The  arterioles  given  off  have  a  straight 
course,  and  are  the  ARTERIOLE  RECIVE.  They  very  soon 
break  up  into  CAPILLARIES  that  surround  the  tubules  of  the 
medulla.  These  continue  as  VENOUS  radicals  that  unite  to 


178  THE    URINARY    SYSTEM. 

form  straight  veins,  VEN^  RECT^:,  which  empty  into  the 
VENOUS  ARCH  on  its  concave  surface. 

The  VENOUS  ARCHES  unite  at  the  columns  of  Bertin, 
and  pass  down  these,  parallel  to  the  arteries,  as  the  INTER- 
LOBAR  VEINS.  In  the  sinus,  they  unite  to  form  the  renal 
'vein. 

The  vessels  of  the  kidney  communicate  with  those  of  the 
perirenal  fat,  through  the  vessels  of  the  capsule.  This  is 
of  importance.  Direct  anastomoses  between  arterial  and 
venous  vessels  occur  in  this  organ. 

The  lymphatics  comprise  a  capsular  set,  cortical  and 
medullary  plexuses.  The  capsular  vessels  empty  into  those 
of  the  cortical  plexus.  These,  in  turn,  empty  into  those  of 
the  medullary  plexus,  the  vessels  of  which  follow  the  blood- 
vessels, emerge  at  the  hilus,  and  pass  to  the  neighboring 
lymph  nodes. 

The  nerves  are  derived  from  both  systems.  They 
follow  the  vessels  and  envelop  them  in  networks  to  the 
smallest  divisions.  Some  supply  the  pelvis,  and  others  pass 
to  the  tubules,  and,  apparently,  enter  the  epithelium. 

THE  EFFERENT  APPARATUS. 

The  Efferent  Apparatus  consists  of  the  Pelvis,  Ureter, 
Bladder  and  Urethra. 

The  Pelvis  is  the  upper,  expanded  portion  of  the  ureter, 
and  lies  in  the  sinus.  It  is  very  irregular  and  is  divided 
into  two  or  three  main  portions,  the  INFUNDIBULA,  or 
CALYCES  MAJOR,  which  are  arranged  in  little  cup-like 
structures  around  the  apices  of  medullary  pyramids. 
These  are  the  CALYCES  MINOR,  and  they  are  equal  in  number 
to  the  pyramids.  The  three  coats,  MUCOUS,  MUSCULAR  and 
FIBROUS,  extend  throughout  the  ureter  and  bladder. 

The  MUCOUS  membrane  consists  of  transitional  cells, 
basement  membrane  and  tunica  propria.  The  epithelial  cells 


PELVIS  OF  THE  URETER. 


179 


are  not  all  regular,  as  those  of  the  transitional  variety  are 
supposed  to  be.  The  upper  cells  are  usually  somewhat 
flattened,  and  almost  squamous.  Beneath  these,  they 
are  somewhat  larger,  and  more  or  less  pear-shaped,  while 
the  lowest  cells  are  polyhedral.  The  tunica  propria  con- 


FIG.  62. 

A.  Cross-section  of  Human  Ureter — a.  lumen;  6.  epithelium;  c.  basement 
membrane;  d.  longitudinal  fold  of  mucosa;  e.  tunica  propria;  /.  inner 
longitudinal  muscle;  g.  outer  circular  muscle;  h.  vessels;  i.  fibrous  coat. 
B.  Cross  Section  of  Segment  of  Human  Bladder — a.  mucous  coat;  b. 
muscular  coat;  c.  fibrous  coat;  d.  transitional  epithelium;  e.  basement 
membrane;/,  tunica  propria;  g.  blood-vessels;  h.  white  fibrous  tissue;  i. 
inner  longitudinal  muscle;  k.  middle  circular  muscle;  /.  white  fibrous 
tissue;  m.  outer  longitudinal  muscle;  n.  venule;  o.  arteriole;  p.  adipose 
tissue. 

sists  of  delicate  fibre-elastic  tissue,  in  which  lymphoid 
tissue  may  be  seen. 

The  MUSCULAR  coat  consists  of  smooth  muscle  fibres  that 
are  not  distinctly  arranged  into  layers. 

The  FIBROUS  coat  is  the  supportive  coat,  and  is  composed 
of  white  fibrous  tissue. 


l8o  THE    URINARY    SYSTEM. 

URETER. 

The  Ureter  is  the  small  tube  connecting  the  kidney  and 
the  bladder,  which  organ  it  enters  at  an  acute  angle.  Its 
coats  are  quite  distinct. 

The  MUCOSA  resembles  that  of  the  pelvis,  with  which  it 
is  continuous.  The  epithelial  cells  have  the  same  appear- 
ance, but  the  tunica  propria  sometimes  sends  delicate  fibres 
up  into  the  epithelial  layer.  These  fibres  lie  between  the 
cells.  In  it  are  found  diffuse  lymphoid  tissue  and  some 
racemose  glands.  The  whole  coat  is  usually  thrown  into 
longitudinal  folds. 

The  MUSCULAR  coat  consists  of  smooth  muscle  tissue, 
arranged  in  definite  layers.  The  inner  consists  of  longi- 
tudinal, and  the  outer  of  circular  fibres.  Occasionally,  at 
the  lower  end,  there  is  added  an  external  longitudinal  layer, 
which  continues  into  the  bladder. 

The  FIBROUS  coat  does  not  differ  from  that  of  the  pelvis. 

BLADDER. 

The  Bladder  is  a  muscular  sac  that  acts  as  a  reservoir  for 
the  urine.  It  consists  of  fundus  or  body,  and  a  small  con- 
stricted portion,  the  neck,  which  continues  as  the  urethra. 

The  MUCOUS  coat  resembles  that  of  the  ureter  in  structure. 
The  cells  may  be  somewhat  flatter.  Often,  in  the  ureter  and 
bladder  of  children  at  birth,  and  older  fetuses,  the  cells  are 
all  of  the  polyhedral  type,  and  represent  a  typic  layer  of 
transitional  cells.  In  urinary  examinations,  it  is  prac- 
tically impossible  to  tell  the  cells  of  the  pelvis,  ureter  and 
bladder  from  one  another.  The  tunica  propria  contains 
diffuse  lymphoid  tissue,  and  even  solitary  follicles,  also 
racemose  glands,  at  times. 

The  mucosa  is  loosely  attached  to  the  muscular  coat,  ex- 
cept at  a  small  triangular  area  near  the  neck.  This  space 


BLADDER.  l8l 

has  for  its  apex  the  urethral  opening,  and  for  its  basal 
angle,  the  ureteral  orifices.  A  line,  connecting  the  two 
latter,  forms  the  base.  This  area  is  the  trigonum  vesicce. 

The  MUSCULAR  coat  is  composed  of  smooth  muscles. 
This  is  arranged  as  inner  longitudinal,  middle  circular  and 
outer  longitudinal  layers.  All  of  the  layers  interlace,  more 
or  less,  thereby  giving  a  peculiar  appearance  to  this  coat. 
At  the  neck,  the  circular  fibres  become  quite  pronounced 
and  constitute  the  sphincter  of  the  bladder. 

The  FIBROUS  coat  supports  the  others,  and  prevents 
undue  dilatation. 

The  blood-vessels  lie  in  the  outer  portion  of  the  tunica 
propria  of  the  above  organs,  and  from  these  a  very  close 
network  of  capillaries  is  formed  beneath  the  epithelium, 
and  in  the  muscular  coat.  These  vessels  are  accompanied 
by  the  lymphatics. 

The  nerves  are  chiefly  sympathetic,  and  ganglia  are  not 
uncommon.  Many  of  the  nerve  fibres  end  beneath  the 
epithelium. 

The  male  Urethra  is  many  times  longer  than  that  of  the 
female.  In  the  female,  the  structure  is  quite  simple, 
and  it  will  be  first  considered. 

The  female  Urethra  is  lined  by  transitional  cells,  except 
at  its  outer  end,  where  the  stratified  squamous  cells  of  the 
skin  enter  into  its  structure.  The  transitional  cells  are 
sometimes  quite  flattened.  Some  writers  describe  a  simple 
columnar  layer  in  the  middle  portion.  The  basement 
membrane  rests  upon  a  papillated  tunica  propria,  in  which 
are  found  the  glands  of  Littre;  these,  in  the  female,  are  not 
very  numerous. 

The  MUSCULAR  coat  consists  of  smooth  muscles,  arranged 
as  inner  longitudinal  and  outer  circular  layers,  separated  by 
an  intermuscular  layer  of  white  fibrous  tissue. 

The  male  Urethra  is  more  complex,  and  is  divided  into 


182  THE    URINARY    SYSTEM. 

three  portions,  PROSTATIC,  the  continuation  of  the  bladder; 
the  MEMBRANOUS,  that  portion  beneath  the  symphysis 
pubis,  and  the  PENILE. 

The  PROSTATIC  part  is  lined  by  transitional  cells  that  are 
continued  from  the  bladder.  In  the  MEMBRANOUS  portion, 
stratified  columnar  cells  are  present,  and  these  become 
simple  in  the  PENILE  division.  Just  before  the  outlet,  or 
meatus,  is  reached,  the  urethra  dilates,  and  this  portion  is 
called  the  fossa  navicularis.  It  is  lined  by  stratified 
squamous  cells.  The  cells  are  all  supported  by  basement 
membrane  and  tunica  propria,  which  consists  of  white 
fibrous  tissue,  in  which  the  glands  of  Littre  are  very 
numerous. 

The  MUSCLE  tissue  is  like  that  of  the  female  urethra, 
and  continues  to  the  penile  portion,  where  it  disappears. 
In  the  membranous  part,  the  muscular  coat  is  reinforced  by 
the  compressor  urethrce  muscle,  which  tapers  toward  the 
prostatic  and  penile  divisions. 

The  FIBROUS  coat  consists  of  white  fibrous  tissue,  and 
strengthens  the  urethra. 

Capillaries  are  numerous  in  the  mucosa,  and  the  vessels 
are  followed  by  the  nerves  and  lymphatics.  The  nerves  end 
in  the  tunica  propria,  just  beneath  the  epithelium. 

The  various  portions  of  the  Urinary  System  are  lined  by 
the  following  cells: 

KIDNEY. 

URINIFEROUS  TUBULE: 

RENAL  CORPUSCLE Simple  squamous. 

NECK        Simple  squamous. 

FIRST  CONVOLUTED  TUBULE     .  Cuboidal  to  columnar. 

DESCENDING  LIMB Simple  squamous. 

LOOP   OF    HENLE Simple  squamous  or   low 

cuboidal. 

ASCENDING  LIMB        Low  cuboidal. 

SECOND  CONVOLUTED  TUBULE    Cuboidal  to  columnar. 


ADRENAL.  183 

ARCHED  CONNECTING  TUBULE    Cuboidal 
STRAIGHT  COLLECTING  TUBULE  Columnar 
PAPILLARY  DUCTS Tall  columnar. 

PELVIS Transitional. 

URETER       Transitional. 

BLADDER Transitional. 

/  Transitional. 

URETHRA.     .FEMALE <  Oj     ,.£    .. 

\  Stratified  squamous. 

MALE 

FIRST  PART Transitional. 

SECOND  PART Stratified  columnar. 

THIRD  PART Simple  columnar. 

FOSSA  NAVICULARIS      ....  Stratified  squamous. 

ADRENAL. 

The  Adrenal,  or  Suprarenal  Body  is  a  ductless  gland.  It 
lies  at  the  upper  pole  of  the  kidney,  and  has  a  yellow  color. 
Upon  section,  it  shows  a  yellow  external  layer,  and  a  dark 
centrum. 

The  organ  is  surrounded  by  a  capsule  of  white  fibrous 
tissue,  in  which  involuntary,  nonstriated  muscle  may  be 
found.  Beneath  this  is  the  parenchyma,  which  consists  of 
Cortex  and  Medulla. 

The  Cortex  consists  of  three  zones  of  epithelial  cells,  the 

ZONA  GLOMERULOSA,   ZONA    FASCICULATA  and  ZONA  RETICU- 
LARIS. 

The  ZONA  GLOMERULOSA  lies  just  beneath  the  capsule, 
and  is  composed  of  several  rows  of  cell-groups,  oval  or  cir- 
cular in  outline,  surrounded  by  capillaries  and  reticulum. 
The  cells,  mostly  large  and  polyhedral,  contain  a  consider- 
able number  of  fat  globules. 

Beneath  this  zone,  the  cells  are  arranged  in  columns  of 
twos,  called  the  ZONA  FASCICULATA.  These  cells  resemble 
the  above,  but  the  nuclei  are  on  the  capillary  side  of  the  cells. 
The  columns  are  separated  from  one  another  by  reticulum, 
supporting  many  capillaries. 


1 84 


THE    URINARY    SYSTI.M. 


The  ZONA  RETICULARIS  is  composed  of  an  irregular  in  l 
work  of  cells   formed  by  the  anastomosis  of   the  columns. 
These  cells  are  usually  smaller  and  outlines  distinct.     The 
nuclei  are  large,  and  the  protoplasm  pigmented. 

The  Medulla  is  usually  separated  from  the  cortex  by  a 
layer  of  large,  smooth  cells.  Beneath  this  layer,  the  cells 
are  arranged  in  irregular  groups,  and  chains  surrounded  by 


I'v^.v'':-" 


FIG.  63. — SECTION  OF  HUMAN  ADRENAL. 

a,  Capsule;  b,  zona  glomerulosa;  c,  zona  fasciculata;  d,  zona  reticularis; 
e,  chromaffin  cells  of  the  medulla;  /,  medullary  vein 

reticulum  and  capillaries.  These  cells  are  small,  and  their 
outlines  are  indistinct.  They  color  very  deeply  with 
chromium  salts  and  are  called  chromaffin  cells.  These 
are  found  in  other  ductless  glands  as  the  hypophysis. 
Nerve  cells  are  also  present. 

The  blood-vessels  are  quite  numerous,  and  apparently  ab- 
sorb the  secretion  of  the  gland.     They  form  a  plexus  in  the 


ADRENAL.  185 

capsule,  from  which  the  arterial  branches  penetrate  the  cor- 
tex, where  they  form  many  capillaries  that  surround  the 
cells  quite  closely.  These  capillaries  empty  into  thin- 
walled  venous  radicals  in  the  outer  portion  of  the  medulla, 
and  from  them  veins  are  formed  that  do  not  anastomose 
with  one  another,  but  empty  into  the  central  veins.  The 
medullary  capillaries  are  derived  from  the  capsular  vessels 
that  pass  to  the  medulla  through  the  cortex  without  branch- 
ing. They  unite  to  form  the  above-named  veins,  which  are 
two  or  four  in  number. 

The  lymphatics  follow  the  blood-vessels  closely.  They 
lie  between  the  cell-groups,  and  even  penetrate  the  columns, 
and  end  between  the  cells. 

The  nerves,  both  myelinated  and  amyelinated,  are 
numerous.  A  plexus  in  the  capsule  sends  branches  into  the 
cortex,  where  plexuses  are  formed  around  the  vessels. 
Branches  pass  from  the  capsular  plexus  to  the  medulla, 
where  rich  plexuses  are  formed  around  the  cells  and  veins. 
Sympathetic  ganglia  are  also  present. 


CHAPTER  XIII. 


THE  MALE  GENITAL  SYSTEM. 

The  Male  Generative  Organs  form  a  very  complex  sys- 
tem They  comprise  the  Testicle,  Epididymis,  Vas  Defer- 
ens,  Seminal  Vesicles,  Ejaculatory  Duct,  Prostate,  Glands 
of  Cowper  and  the  Penis. 

The  Testicle  is  another  compound  tubular  gland.  It  is 
surrounded  by  an  unusually  thick  CAPSULE  called  the 
TUNICA  ALBUGINEA,  which  is  composed  of  bundles  of  white 
fibrous  tissue  that  interlace  so  as  to  form  a  very  tough 
and  prominent  covering.  From  its  inner  surface,  prolonga- 
tions, or  trabeculce,  pass  into  the  center  of  the  organ  to 
divide  it  irregularly  into  compartments.  These  trabeculae 
all  converge  at  the  dorsal  portion  of  the  organ,  where  the 
capsule  is  very  thick,  forming,  at  this  point,  a  thickened 
mass  called  the  CORPUS  HIGHMORI,  OR  MEDIASTINUM 
TESTIS.  Here  a  number  of  tubules,  to  be  described  later, 
are  found. 

The  TUNICA  VAGINALIS  TESTIS  is  a  SEROUS  MEMBRANE  that, 

at  one  time,  was  continuous  with  the  peritoneum.  It 
covers  almost  the  entire  organ,  and  is  attached  to  the  tunica 
albuginea,  and  constitutes  the  visceral  layer  of  the  tunica 
vaginalis.  It  is  reflected  over  the  inner  surface  of  the 
scrotum  as  the  parietal  layer.  Some  writers  consider  this 
membrane  part  of  the  tunica  albuginea,  and  describe  it  as 
such,  but  as  it  is  genetically  different,  it  should  be  considered 
a  separate  covering. 

The  PARENCHYMA  of  the  testicle  is  made  up  of  TUBULES, 

186 


TESTICLE. 


I87 


which,  like  those  of  the  kidney,  are  very  convoluted,  and 
consist  of  secretory  and  conductive  portions.  These  tubules 
are  the  SEMINIFEROUS  TUBULES,  and  are  collected  into 
groups  which  correspond  to  lobules.  These  groups, 
limited  by  the  connective  tissue  of  the  tunica  albuginea 


FIG.  64. — HUMAN  TESTICLE. 

A.  Peripheral  portion  of  the  testicle  showing  the  capsule  and  tubules — a. 
tunica   albuginea;    b.    blood-vessel;    c.    membrana   propria   of   tubule; 

d.  interstitial    cells;    e.  spermiogenetic  cells;  /.  lumen  of    longitudinal 
tubule.     B.   Single    seminiferous    tubule   highly  magnified — a.    tunica 
propria;  b.  basement   membrane;   c.  spermiogonia;   d.  cells  of   Sertoli; 

e.  mother    and    daughter    cells;    /.   spermids;    g.  spermia.     C.   Sper- 
mia  highly  magnified.     D.  Tubule  of  the  epididymis. 

that  extends  to  the  corpus,  constitute  the  COMPARTMENTS 
of  the  testicle. 

The    COMPARTMENTS    contain   a  large    number  of    very 
convoluted  tubules,  in  which  the  SPERMIA  are  formed;  these 


1 88  THE    MALE    GENITAL    SYSTEM. 

are  the  SEMINIFEROUS  TUBULES  proper,  and  they  are 
supposed  to  end  blindly  beneath  the  capsule.  According 
to  some,  however,  they  anastomose,  and  so  form  a  set  of 
communicating  tubules,  which  pass  toward  the  apex  of  a 
compartment.  There  are  said  to  be  three  to  four  con- 
voluted tubules  in  each  compartment,  or  about  600  in  the 
testicle.  When  straightened  each  measures  about  2  feet 
in  length.  At  the  apex  of  a  compartment  these  convoluted 
tubules  unite  to  form  a  smaller  number  of  straight  tubules 
that  are  conductive  in  function.  These  are  the  TUBULI 
RECTI,  which  pass  into  the  mediastinum,  where  they  anasto- 
mose to  form  a  network  called  the  RETE  TESTIS.  In  the 
upper  portion  of  the  mediastinum,  these  tubules  join  to 
form  a  few,  ten  to  fifteen,  vessels  that  pass  toward  the 
edge  of  the  corpus  Highmori,  as  the  VASA  EFFERENTIA. 
As  these  leave  the  testicle,  they  become  convoluted  and 
dilated  into  cone-shaped  structures  called  the  CONI 
VASCULOSA,  or  GLOBUS  MAJOR,  of  the  epididymis.  The 
CONI  VASCULOSA  unite  to  form  a  single  tubule  that  runs 
a  very  convoluted  course,  forming  a  narrow  continuation 
of  the  above,  called  the  BODY  of  the  epididymis.  At 
the  lower  pole  of  the  testicle,  the  mass  formed  by  the 
continuation  of  the  body  is  somewhat  larger,  and  is  named 
the  GLOBUS  MINOR.  The  tubule  that  continues  from  this 
point  into  the  abdomen  is  called  the  VAS  DEFERENS. 

The  SEMINIFEROUS  TUBULES  are  from  140  to  200  microns 
in  diameter,  and  form  the  bulk  of  the  testicle.  Each  con- 
sists of  a  small  amount  of  tunica  propria,  and  a  basement 
membrane,  upon  which  is  found  a  number  of  layers  of  cells. 
The  basal  layer  consists  of  two  varieties,  the  SPERMIO- 
GONIA,  which  are  the  more  numerous,  and  the  SUSTENTACU- 

LAR  CELLS,  Or  COLUMNS  OF  SERTOLI. 

The  SPERMIOGONIA  are  rather  large  cells,  in  which  the 
nuclei  are  mostly  in  the  resting  stage.  The  cells  just  within 


TESTICLE.  189 

these  are  derived  from  the  spermiogonia,  and  are  the 
MOTHER  CELLS.  Each  mother  cell  divides  in  two  daughter 
cells,  which,  in  turn,  give  rise  to  the  SPERMIDS,  from  which 
the  SPERMIA  are  developed.  These  layers  are  not  regular, 
as  the  space  within  the  lumen  is  gradually  filled  by  the 
reproducing  cells. 

The  COLUMN  of  SERTOLI,  or  SUSTENTACULAR  CELL  is  a  less 
distinct  element.  It  is  pyramidal  in  shape,  and  extends  up 
through  the  various  layers,  and  serves  as  a  support  for  the 
cells  that  are  being  transformed  into  spermia.  For  this 
reason,  it  has  received  the  name  of  SUSTENTACULAR  CELL. 
Its  protoplasm  is  usually  clear,  though  it  may  contain 
pigment  granules.  Its  nucleus  is  pale,  but  the  nucleolus  is 
quite  prominent.  These  cells  are  said  to  divide  amitotic- 
ally.  It  plays  an  important  part  in  spermiogenesis. 

Between  the  tubules  lies  the  INTERSTITIAL  CONNECTIVE 
TISSUE  that  supports  the  blood-vessels,  nerves  and  lymph- 
atics. It  is  the  variety  of  connective  tissue  called  reticulum, 
and  here  and  there  are  found  groups  of  large  cells  that  con- 
tain coarse  granular  protoplasm.  These  are  the  INTERSTI- 
TIAL CELLS,  or  CELLS  OF  LEYDic.  The  protoplasm  often 
contains  pigment,  fat  and  crystalloids.  These  cells  are 
probably  embryonal  remains.  They  are  most  numerous 
before  and  after  the  period  of  sexual  activity. 

The  EXCRETORY  SYSTEM  starts  with  the  TUBULI  RECTI. 
These  are  from  25  to  50  microns  in  diameter,  and  extend  to 
the  apex  of  the  compartment.  They  are  lined  by  simple 
cuboidal,  or  squamous,  cells  that  rest  upon  a  basement 
membrane. 

The  RETE  TESTIS  consists  of  a  network  formed  from  the 
tubuli  recti,  and  lies  in  the  MEDIASTINUM.  These  tubes 
have  a  somewhat  larger  diameter  than  the  foregoing,  but 
are  lined  by  the  same  variety  of  cells. 

The  VASA  EFFERENTIA  are  few  in  number,  and  are  formed 


\()0  TIIK   MALI;  GENITAL  SNSTK.M. 

by  a  union  of  the  tubules  of  the  rete  testis.  The  lining  cells 
are  rather  peculiar  in  that  in  some  areas  they  are  simple 
ciliated,  while  in  others,  nonciliated.  The  basement  mem- 
brane is  further  supported  by  interstitial  tissue  that  contains 
some  circularly  arranged  nonstriated  muscle  tissue. 

The  Epididymis  consists  of  a  mass  of  convoluted  tubules 
that  lie  outside  of  the  testicle.  It  is  divided  into  three  por- 
tions, the  globus  major,  or  head,  the  body,  and  the  globus 
minor,  or  tail.  The  globus  major  consists  of  10  to  15  large, 
cone-shaped  tubules  that  are  very  convoluted .  These  tubules 
are  the  continuations  of  the  vasa  efferentia.  The  cilia  are 
the  largest  in  the  body.  The  body  and  tail  consist  of  a 
single  long  tubule  that  is  very  convoluted;  if  straightened 
it  would  measure  19  to  20  feet  in  length. 

The  epididymis  is  surrounded  by  a  dense  sheath,  or  cap- 
sule of  white  fibrous  tissue  that  divides  it  into  compart- 
ments. In  the  globus  major,  the  tubules  in  a  compart- 
ment represent  the  convolutions  of  one  of  the  coni 
vasculosa. 

The  tubules  are  lined  by  STRATIFIED  CILIATED  CELLS  that 
rest  upon  a  basement  membrane,  outside  of  which  is  a  dis- 
tinct tunica  propria.  External  to  this  a're  two  layers  of 
smooth  muscle  tissue,  one  circularly,  and  the  other  (thin) 
longitudinally,  arranged. 

The  vessels  of  the  testicle  enter  the  corpus  Highmori  and 
inner  layer  of  the  tunica  albuginea,  and  send  branches 
around  the  convoluted  tubules,  especially,  forming  dense 
plexuses. 

The  lymphatics  originate  in  the  capsule  and  around  the 
seminiferous  tubules,  and  pass  to  the  corpus,  and  leave  the 
testicle  from  that  point. 

The  nerves  are  chiefly  sympathetic,  but  possess  no  ganglia. 
These  form  plexuses  around  the  vessels  and  the  tubules. 
Occasionally,  ganglia  are  found  in  the  epididymis. 


SPERMATOZOON.  191 

The  Spermatozoon,  or  Spermium,  consists  of  three  main 
parts,  head,  middle -piece  and  tail  (see  Fig.  65). 

The  head  is  somewhat  pear-shaped  when  viewed  from  the 
side  and  is  4  to  5  microns  long  and  2  to  3  microns  wide.  It 
consists  of  the  condensed  chromatin  of  the  spermium  con- 


FIG   65. — DIAGRAM  OF  THE  DEVELOPMENT  OF  SPERM  IA 

(Stohr  after  Meves). 

a.c.,  Anterior  centrosome;  a./.,  axial  filament;  c. p.,  middle  piece;  ch,p., 
tail;  n,  nucleus;  nk,  neck;  p,  protoplasm;  p.  c.,  posterior  centrosome. 

stituting  8  or  12  chromosomes.  It  is  surrounded  by  a 
delicate  layer  of  protoplasm.  In  some  mammals  a  little 
body  is  seen  at  the  front  part  of  the  head  just  beneath  the 
enveloping  protoplasm;  this  is  the  acrosome  and  it  represents 
the  attraction  sphere  of  a  centrosome.  This  end  of  the 
spermium  represents,  apparently,  a  cutting  edge,  and  in 


IQ2  THE    MALE    GENITAL   SYSTEM. 

some  lower  forms  it  possesses  a  spiral  or  barbed  projection 

that  assists  in  the  entrance  of  the  spermium  into  the  ovum. 

The  middle-piece  is  composed  of  several  portions,   the 

END-KNOB,     AXIAL     FIBRE,     SPIRAL     FIBRE     and      ENVELOP. 

The  END-KNOB  connects  the  head  with  the  middle-piece 
and  is  also  called  the  NECK.  Here  is  seen  the  divided 
centrosome,  one  part  of  which  becomes  a  flattened  mass 
at  the  junction  of  head  and  middle-piece;  the  other  elon- 
gates into  the  AXIAL  FIBRE  with  its  front  end  enlarged  to 
a  disc-like  mass  that  ultimately  separates  from  the  axial 
fibre  to  surround  it  as  a  darkly  staining  ring.  Surround- 
ing the  axial  fibre  is  a  delicate  SPIRAL  FILAMENT  that  is 
probably  derived  from  the  protoplasm.  The  ENVELOP  is  a 
thin  layer  of  protoplasm  that  surrounds  the  middle-piece 
and  is  continued  over  the  head  and  tail  portions  of  the 
spermium. 

The  tail  consists  of  AXIAL  FIBRE  and  ENVELOP.  The 
AXIAL  FIBRE  is  the  continuation  of  the  axial  fibre  of  the 
middle-piece,  but  is  not  so  prominent.  It  represents  an 
elongated  centrosome.  It  forms  the  motile  portion  of  the 
organism  and  its  origin  from  a  centrosome  is  not  difficult 
to  understand  when  we  consider  that  in  ameboid,  flagel- 
lated and  ciliated  cells  the  centrosome  presides  over  the 
property  of  motion.  It  is  about  5  microns  longer  than 
the  envelop.  The  ENVELOP  represents  a  thin  protoplasmic 
covering  of  the  axial  fibre  and  is  continuous  with  that  of  the 
middle-piece.  The  tail  is  about  40  to  50  microns  long  and 
about  i  micron  in  diameter. 

Spermiogenesis  is  that  peculiar  change  by  which  spermia 
are  formed  from  cells  several  generations  removed  from  the 
spermiogonia,  or  original  cells.  The  spermiogonia,  with 
the  columns  of  Sertoli,  form  the  basal  layer  of  cells  of  the 
seminiferous  tubule.  Up  to  the  age  of  puberty,  these 
tubes  are  usually  solid,  or  nearly  so. 


SPERMATOGENESIS.  193 

The  Spermiogonia  represent  the  primordial  cells,  and 
by  division  give  rise  to  the  mother  cells,  or  spermiocytes. 
These  latter  give  rise  to  the  daughter  cells,  and  these  form 
the  spermids,  which,  by  a  direct  change,  become  spermia. 
In  this  last  division,  the  chromosomes  are  reduced  from 
twenty-four  to  twelve  (or  from  sixteen  to  eight) .  Upon  fertili- 
zation, these  twelve  unite  with  the  twelve  within  the 
ovum,  reduced  from  twenty-four  to  form  the  twenty-four 
found  in  all  cells  that  are  derived  from  the  segmenting 
ovum. 

In  the  formation  of  spermia,  the  spermids  are  of  the  most 
importance.  According  to  some  authors,  the  nucleus 
forms  the  whole  organism,  while  others  hold  the  head  and 
middle-piece  are  of  nuclear  origin,  and  the  tail  protoplasmic. 
These  cells  become  crowded  or  drawn  to  the  columns  of 
Sertoli,  to  which  they  apparently  attach  themselves.  At 
the  same  time,  the  shape  of  the  cell  becomes  modified  by 
elongation.  The  CHROMATIN  of  the  nucleus  becomes  denser 
and  migrates  toward  the  attached,  or  peripheral  end,  while 
the  protoplasm  draws  toward  the  central  end.  At  the 
attached,  or  peripheral  end,  the  nucleus  has  a  small  promi- 
nence developed  that  indicates  the  future  head.  The  proto- 
plasm becomes  clear  and  draws  centrally,  forming  a  slender 
vesicle,  in  the  middle  of  which  a  delicate  line  appears. 
This  line  joins  the  head,  and,  growing  backward,  breaks 
through  the  membrane  to  form  the  TAIL  of  the  spermium. 

The  CENTROSOMES,  usually  two  in  number,  become  differ- 
ent in  shape;  the  attraction  sphere  of  the  smaller  passes  to 
the  head  of  the  spermium  to  become  the  ACROSOME.  The 
smaller  centrosome  then  becomes  disc-shaped  and  attaches 
itself  to  head  at  its  junction  with  the  middle-piece;  the  larger 
is  cone-shaped,  and  differentiates  into  two  portions,  the 
larger  of  which  passes  toward  the  nucleus,  and  develops  a 
flattened  extremity  just  behind  the  preceding;  the  remain- 


194  THE    MALE    GENITAL    SYSTEM. 

der  elongates  into  the  axial  fibre  of  the  middle-piece  and 
tail.  The  ENVELOP  is  held  to  be  protoplasmic  in  origin. 

As  the  spermia  continue  to  develop,  the  column  of 
Sertoli  increases  in  length,  and  when  development  is  com- 
plete, the  organisms  lie  in  the  lumen  of  the  tubule.  The 
column  of  Sertoli,  with  the  attached  spermids,  is  called  a 
SPERMIOBLAST.  Loisel  believes  that  these  columns  secrete 
a  substance  that  attracts  the  spermids  (positive  chemiotaxis) . 

The  Semen  consists  principally  of  spermia  suspended  in  a 
fluid  derived  from  the  various  portions  of  the  genital  tract. 
The  spermia  are  practically  amotile  until  mixed  with  the 


FIG.  66. — HUMAN  SPERMIA. 

i.  Surface  view;  2.  side  view;  3.  looped  seminal  filament;  4.  spermium  of 
an  ox;  a.  head;  b.  middle  piece;  c.  tail. 

secretion  of  the  prostate,  when  they  become  actively  motile. 
Beside  the  PROSTATIC  FLUID,  other  secretion  is  added 
by  the  seminal  vesicles,  glands  of  Cowper  and  urethral 
glands  (Littre).  In  addition  to  the  spermia,  crystals  and 
amyloid  bodies  from  the  prostate,  fat  globules  and  epithelial 
cells  are  seen  in  the  semen.  There  are  said  to  be  about 
60,000  spermia  in  each  cu.  mm.  of  semen. 

Motility  may  be  exhibited  by  the  spermia  twenty-four 
hours  after  death.  They  have  been  kept  alive  for  two 
weeks,  under  proper  conditions,  and  this  may  readily  occur 
in  the  female  genital  tract.  Water,  acids  and  metallic 


VAS    DEFERENS   AND    SEMINAL    VESICLES.  195 

salts  cause  cessation  of  action,  while  alkaline  and  normal 
salt  solutions  aid  it.  Batelli,  in  1902,  found  by  experi- 
ments that  the  spermia  travel  better  against  than  with  the 
current. 

The  Vas  Deferens  connects  the  testicle  with  the  urethra. 
It  passes  into  the  body  through  the  inguinal  canal,  and  is 
accompanied,  to  the  internal  ring,  by  the  spermatic  artery 
and  vein,  the  deferential  artery,  cremaster  muscle  and 
fibrous  connective  tissue.  These  form  the  SPERMATIC  CORD. 

THE  VAS  DEFERENS. 

The  Vas  has  three  coats,  MUCOUS,  MUSCULAR  and  FIBROUS. 

The  MUCOUS  coat  consists  of  stratified  columnar  cells 
resting  upon  basement  membrane  and  tunica  propria.  It 
is  usually  thrown  into  longitudinal  folds.  The  cells  in  the 
first  portion  may  be  stratified  ciliated  continued  from  the 
epididymis. 

The  MUSCULAR  coat  is  composed  of  smooth  muscle  tissue 
usually  arranged  as  inner  and  outer  longitudinal  and  middle 
circular  layers.  These  are  not  always  distinct,  as  they  may 
interlace,  more  or  less. 

The  FIBROUS  coat  consists  of  fibro-elastic  tissue,  and  gives 
strength  to  the  organ. 

THE  SEMINAL  VESICLES. 

The  Seminal  Vesicles  lie  beneath  the  bladder,  and  empty 
into  the  vas  through  the  SEMINAL  DUCTS.  They  consist  of 
three  coats,  MUCOUS,  MUSCULAR  and  FIBROUS. 

The  MUCOUS  coat  is  lined  by  simple  columnar,  or  pseudo- 
stratified,  cells  that  possess  yellow  pigment  granules.  These 
cells  rest  upon  basement  membrane  and  tunica  propria. 
The  whole  coat  is  thrown  into  waves,  or  folds,  to  which  an 
apparent  stratification  of  the  cells  is  due. 


196  THE   MALE    GENITAL   SYSTEM. 

The  MUSCULAR  coat  consists  of  inner  circular  and  outer 
longitudinal  layers  of  the  smooth  variety. 

The  FIBROUS  coat  is  indistinct. 

These  organs  act  as  reservoirs  for  spermia,  at  times, 
besides  secreting  a  fluid  that  helps  to  make  up  the  semen. 

The  Ejaculatory  Ducts  are,  in  reality,  the  continuation  of 
the  vas.  They  are  lined  by  simple  columnar  cells,  like  the 
seminal  vesicles.  The  muscle  tissue  is  chiefly  longitudinally 
arranged. 

THE  PROSTATE. 

The  Prostate  is  a  branched  tubular  gland.  It  is  sur- 
rounded by  a  CAPSULE,  and  is  composed  of  three  main  lobes. 
The  CAPSULE  consists,  externally,  of  a  thin  layer  of  white 
fibrous  tissue,  beneath  which  is  a  thick  layer  of  smooth 
muscle  tissue.  From  the  latter,  trabeculae  pass  into  the 
center  of  the  organ,  and  converge  at  the  urethra.  They 
possess  thick  bases,  but  taper  as  the  center  is  approached. 
These  partitions  form  COMPARTMENTS  in  which  the  GLANDS 
are  found. 

The  GLANDS  are  of  the  branched  tubular  variety,  and  the 
ALVEOLI,  or  SECRETORY,  PORTIONS  are  lined  by  simple  colum- 
nar cells,  and  are  separated  from  one  another  by  the  mus- 
cular trabeculcE.  The  basal  portions  of  the  cells  contain 
granules  that  have  an  affinity  for  the  acid  stains.  The  ducts 
are  a  dozen  or  so  in  number,  and  are  lined  by  simple 
columnar  cells,  except  at  their  outer  ends,  where  transitional 
cells  of  the  urethra  are  found.  These  ducts  empty  into 
the  floor  of  the  urethra.  The  alveoli  contain  a  varying 
number  of  structures  called  amyloid  bodies;  these  are  few 
in  youth  and  numerous  in  old  age. 

The  vessels  that  supply  the  tubules,  ramify  in  the  muscu- 
lar septa,  and  form  plexuses  of  capillaries  that  surround  the 


PROSTATE.  197 

tubules.     The  veins  run  toward  the  periphery,  and  form  a 
network  in  the  capsule. 

The  lymphatics  originate  in   the  septa,   and  follow  the 
vessels. 


FIG.  67. — SECTION  OF  THE  PROSTATE  GLAND. 

a.  Interstitial  tissue  and  muscular  trabecula;  b.  capsule;  c.  glands;  d.  prostatic 
bodies;  e.  secretion;/,  blood-vessel;  g.  duct. 

Nerve  fibres  are  numerous,  and  some  special  sensor  organs 
are  present. 

The  Glands  of  Cowper  are  racemose  glands  that  empty 
into  the  penile  portion  of  the  urethra.  They  are  surrounded 
by  a  capsule  of  white  fibrous  tissue  that  divides  the  gland 
into  lobes  and  lobules.  The  alveoli  that  make  up  a  lobule 


198  THE    MALE    GENITAL   SYSTEM. 

are  lined  by  low  columnar  mucous  cells.  These  rest  upon 
basement  membrane  and  tunica  propria.  The  smaller 
ducts  are  lined  by  cuboidal  cells,  while  the  larger  possess 
stratified  columnar  cells.  Bundles  of  muscle  fibres  are 
present. 

THE  PENIS. 

The  Penis  is  a  peculiar  organ  surrounded  by  a  loosely 
attached  skin.  The  latter  contains  no  adipose  tissue.  The 
skin  extends  over  the  end  of  the  organ  as  the  PREPUCE, 
which  is  covered,  upon  both  surfaces,  by  stratified  squam- 
ous  cells.  The  inner  surface  possesses  the  characteristics 
of  a  mucous  membrane. 

The  organ  consists  of  two  main  portions,  the  glans  and 
the  body. 

The  glans  is  covered  by  stratified  squamous  cells,  and  is 
separated  from  the  body  by  a  narrow  constricted  area,  the 
CERVIX.  At  this  point,  the  squamous  cells  of  prepuce  and 
glans  are  continuous. 

The  body  consists  of  two  CORPORA  CAVERNOSA  and  the 
single  CORPUS  SPONGIOSUM. 

The  CORPORA  CAVERNOSA  lie  side  by  side,  forming  the 
dorsal' portion  of  the  penis,  and  are  bound  together  by  a 
thick  sheath  of  white  fibrous  tissue  called  the  tunica  albu- 
ginea.  From  the  inner  surface  of  this,  trabecula  pass  in- 
ward and  form  a  series  of  communicating  spaces,  or  caverns. 
These  are  venous  blood  spaces.  The  trabeculae  contain  tor- 
tuous arteries,  the  helicine  arteries,  which,  when  engorged, 
become  straightened  as  the  organ  increases  in  size.  The 
spaces  become  filled  with  blood,  and,  with  the  vascular 
trabeculae,  constitute  true  erectile  tissue.  This  engorgement 
produces  the  erection.  False  erectile  tissue  depends  for 
its  action  upon  smooth  muscle  tissue. 


PENIS.  199 

The  CORPUS  SPONGIOSUM  has  a  thin  tunic,  and  consists  of 
two  portions,  urethral  and  peripheral.  The  urethral  part  is 
quite  dense  and  rich  in  veins,  while  the  peripheral  part  re- 
sembles, somewhat,  the  cavernous  portion. 

The  glans  is  a  continuation  of  the  corpus  spongiosum, 
and  consists  of  a  delicate  network  of  connective  tissue  en- 
closing a  number  of  small  spaces.  It  is  covered  by  a  deli- 
cate skin,  which  is  continuous  with  the  prepuce,  or  foreskin. 
In  the  cervix  are  located  a  number  of  glands  that  secrete  the 
smegma.  These  are  the  glands  of  Tyson,  or  glandule 
oderiferce. 

The  blood-vessels  and  spaces  are  numerous.  The  arterial 
branches  follow  the  septa,  in  which  they  run  such  a  convo- 
luted course  as  to  receive  the  name  of  helicine  arteries. 
They  form  capillary  plexuses  in  the  trabeculae,  some  of 
which  empty  into  the  spaces,  while  others  pass  over  into 
the  veins.  The  branches  within  the  tunica  form  capillaries 
that  empty  into  the  spaces.  Anastomoses  between  arterial 
and  venous  capillaries  are  numerous. 

The  emissary  veins  receive  blood  from  the  tunica  and 
superficial  vessels,  and  partly  from  the  deeper  tissues  and 
vessels;  they  pass  through  the  tunica  to  empty  into  the 
dorsal  vein  of  the  penis  that  lies  in  a  groove  between  the 
corpora  cavernosa.  These  veins  are  pressed  upon  when  the 
superficial  vessels  are  filled  with  blood,  in  that  way  pre- 
venting egress,  but  not  ingress,  of  the  blood. 

Nerve  organs  include  corpuscles  of  Meissner,  bulbs,  genital 
corpuscles,  Pacinian  bodies  and  intra-epithelial  free  be- 
ginnings. 

The  Paradidymis,  or  organ  of  Giraldes,  is  found  in  the 
epididymis.  It  consists  of  a  number  of  tubules,  in  which 
the  lining  cells  are  low  columnar  or  even  ciliated.  The 
tubules  are  closed,  and  are  separated  from  one  another  by 
vascular  connective  tissue. 


200  THE    MALE    GENITAL   SYSTEM. 

The  cells  that  line  the  various  portions  of  the  male  genital 
tract  are  as  follows: 

Testicle. 

(  Spermiogonia        \ 
0  >   Basal  layer. 

Sustentacular        J 

Spermiocvtes,  or  mother  cells. 

SEMINIFEROUSTUBULE       .      . 

becond  layer. 

Daughter  cells,  Third  layer. 
[  Sperm  ids,    Fourth    layer. 

TUBULI  RECTI Cuboidal  or  squamous. 

RETE  TESTIS       Cuboidal  or  squamous. 

VASA  EFFERENTIA Columnar  or  ciliated. 

Epididymis      Stratified  ciliated. 

,,     T.    .  /  Stratified  columnar. 

VasDeferens       {  _ 

[  Stratified  cdiated  (some). 

Seminal  Vesicles Simple   or   pseudostratified    col- 
umnar. 
Ejaculatory  Duct        Simple  columnar. 


CHAPTER  XIV. 


THE  FEMALE  GENITAL  SYSTEM. 

This  system  consists  of  the  Ovary,  Oviduct,  Uterus, 
Vagina,  Glands  of  Bartholin  and  Genitalia. 

The  Ovary,  the  distinctive  female  organ,  lies  upon  the 
dorsal  surface  of  the  broad  ligament  and  projects  into  the 
pelvic  cavity.  It  is  surrounded  by  a  CAPSULE  of  white 
fibrous  connective  tissue  called  the  TUNICA  ALBUGINEA. 
This  is  not  so  prominent  as  that  of  the  testicle.  The  free 
surface  of  the  capsule  is  covered  by  low  columnar  cells 
called  the  GERMINAL  EPITHELIUM. 

The  organ  consists  of  Cortex  and  Medulla. 

The  Cortex  is  the  outer  part,  and  surrounds  the  medulla, 
except  at  one  point,  at  which  the  vessels  enter  and  leave; 
this  is  the  HILUM,  and  here  the  medulla  comes  to  the  surface. 
The  cortex  is  the  glandular  portion,  where  the  cellular 
elements  of  the  secretion,  the  OVA,  are  formed.  It  consists 
of  a  delicate  reticulum,  the  STROMA,  in  which  the  GRAAFIAN 
FOLLICLES  are  found,  CORPORA  LUTEA  in  various  stages,  and 
occasionally  groups  of  large,  polygonal  epithelial  cells, 
called  the  INTERSTITIAL  CELLS.  The  free  surface  of  the 
stroma  is  covered  by  the  modified  mesothelial  cells,  the 
GERMINAL  EPITHELIUM,  from  which  the  ova  are  derived. 
These  cells  are  low  columnar  elements. 

The  Graafian  follicles  are  characteristic  structures. 
They  vary  in  size;  the  smallest  are  just  beneath  the  tunica 
albuginea,  the  medium-sized  near  the  medulla,  and  the 
largest  extend  from  the  medulla  to  the  capsule,  and  cause  a 
projection  upon  the  surface  of  the  organ. 

201 


202 


THE    FEMALE    GENITAL    SYSTEM. 


Externally  the  FOLLICLE  is  covered  by  a  layer  of  condensed 
stroma  called  the  THECA  FOLLICULI;  the  outer  portion  of  this 
is  called  the  TUNICA  FIBROSA,  and  the  inner  the  TUNICA  VAS- 
CULOSA.  The  THECA  is  lined  by  a  number  of  layers  of 
granular  cells  termed  the  ZONA  GRANULOSA,  within  which  is 


FIG.  68. — CROSS-SECTION  OF  OVARY  OF  A  CAT. 

The  Graafian  follicles  are  so  numerous  that  but  little  of  the  medulla  is  seen. 
a.  Germinal  epithelium;  b.  tunica  albuginea;  c.  immature  Graafian  follicle; 
d.  ovum;  e.  cortical  stroma;  /.  interstitial  cells;  g.  theca  folliculi;  h. 
zona  granulosa;  i.  antrum  containing  liquor  folliculi;  k.  discus  proligerus; 
/.  corona  radiata;  m.  zona  pellucida;  n.  vitellus;  o.  germinal  vesicle;  p. 
follicle  without  ovum;  r.  hilum;  s.  medulla  showi  g  the  tubules  of  the 
parovarium;  t.  arteriole;  u.  venule. 

a  space,  the  ANTRUM,  filled  by  a  liquid,  the  LIQUOR  FOLLIC- 
ULI. At  one  point,  the  granule  layer  projects  into  the 
antrum,  and  this  mass  contains  the  ovum.  This  projection 
is  called  the  DISCUS  PROLIGERUS,  or  CUMULUS  OVIGERUS. 
Just  within  the  granule  cells  of  the  discus  is  seen  a  layer  of 


OVARY.  203 

long  columnar  cells,  the  CORONA  RADIATA.  These  cells 
rest  upon  a  thick  homogeneous  membrane  called  the  ZONA 
PELLUCIDA,  which  is  separated  from  the  ovum  by  a  small 
space,  called  the  PERIVITELLINE  SPACE.  This  space  is 
disputed  by  some  writers.  The  corona  is  supposed  to 
give  rise  to  the  zona  pellucida.  The  OVUM  that  lies  just 
within  the  space  consists  of  a  cell- wall,  the  VITELLINE 
MEMBRANE,  and  cell-body,  the  VITELLUS.  In  the  vitellus 
is  seen  the  nucleus,  or  GERMINAL  VESICLE,  which  contains 
the  prominent  nucleolus,  or  GERMINAL  SPOT. 

The  Ovum  is  the  most  characteristic  and  largest  cell  in 
the  body.  Its  diameter  varies  from  .2  to  .3  mm.  The  zona 
pellucida  that  surrounds  it  is  quite  thick,  measuring  from 
7  to  10  microns.  It  is  said  to  contain  small  radial  canals 
called  micropyles,  through  which  the  spermium  gains  en- 
trance to  the  ovum  in  fertilization.  The  protoplasm  con- 
sists of  yolk  granules,  the  NUTRITIVE  YOLK,  or  DEUTOPLASM, 
and  the  FORMATIVE  YOLK.  The  nucleus  averages  about  30 
microns,  is  eccentrically  placed  and  sharply  outlined  by  a 
membrane  that  possesses  a  double  contour.  The  chroma- 
tin  is  rather  scant,  but  the  nucleolus  is  quite  large  and 
prominent.  The  centrosome  may  be  seen  in  ova  that  have 
not  undergone  maturation.  If  this  process  has  been  com- 
pleted the  centrosome  disappears.  Hertwig  states  that 
they  are  found  in  ova  of  rabbits  up  to  six  or  seven  weeks 
of  age,  and  in  young  guinea-pigs. 

The  Graafian  follicles,  of  which  there  are  about  36,000 
in  each  ovary,  are  developed  during  intrauterine  life,  and 
all  are  usually  present  at  birth.  Not  all  of  these  develop,  by 
any  means.  The  smallest  consist  of  the  OVUM,  surrounded 
closely  by  a  few  layers  of  small  GRANULE  CELLS  and  a 
delicate  THECA.  They  lie  just  beneath  the  tunica  albu- 
ginea,  and  show  no  antrum.  The  medium-sized  follicles 
lie  near  the  medulla,  and  present  an  antrum.  The  GRANULE 


204 


THE    FEMALE    GENITAL    SYSTEM. 


CELLS  are  more  numerous,  and  the  OVUM  larger.  The  fully- 
developed  follicles  extend  from  the  medulla  through  the 
cortex  beyond  the  original  surface  level,  projecting  varying 
distances. 


cr 


zp 


y 


FIG.  69.— OVUM  OF  A  WOMAN  THIRTY  YEARS  OF  AGE,  (McMnrrick). 

cr,  Corona  radiata;  zp,  zona  pellucida;  p,  protoplasmic  zone  of  ovum; 
ps,  perivitelline  space;  y,  yolk  (deutoplasm) ;  n,  nucleus  (germinal  vesicle) 
showing  germinal  spot. 

The  FOLLICULAR  CELLS  are  derived  from  the  germinal  epi- 
thelium, and  grow  into  the  stroma  in  long  columns  during 
the  developmental  period,  as  the  EGG-TUBES  OF  PFLUEGER. 
In  such  a  column  will  be  found  several  large,  and  a  great 


MATURATION.  205 

number  of  small  cells.  These  columns  become  separated 
into  a  number  of  groups  of  cells  consisting  of  one  or  more 
large,  and  many  small  cells.  The  large  are  the  OOGENETIC, 
and  the  small  the  GRANULE  cells.  Gradually,  the  large 
cells  fuse  to  form  a  single  mass  of  protoplasm,  and  all  the 
nuclei,  except  one,  disintegrate.  The  single  cell  resulting 
is  called  the  OOCYTE.  The  egg-tubes  are  separated  into 
these  groups  by  the  stroma  that  grows  into  the  columns. 
This  stroma  further  condenses  around  each  group  to  form 
the  PRIMITIVE  THECA.  Toward  the  age  of  puberty,  these 
follicles  begin  to  develop,  though  they  may  start  sooner. 
The  granule  cells  increase  rapidly  in  number,  and  some  of 
the  more  central  ones  disappear  by  disintegration  or  lique- 
faction. This  gives  rise  to  the  space,  or  ANTRUM,  which  be- 
comes filled  by  a  liquid,  the  LIQUOR  FOLLICULI.  The  latter 
is  probably  derived  from  the  blood-vessels. 

As  the  follicle  develops  and  is  about  to  rupture,  the  OVUM 
(OOCYTE)  undergoes  a  process  called  Maturation. 

Maturation  is  the  process  by  which  the  POLAR  BODIES  are 
formed  and  extruded.  The  germinal  vesicle  migrates 
toward  the  periphery,  and  undergoes  mitotic  change.  When 
the  NUCLEAR  SPINDLE  is  formed  parallel  to  one  of  the  radii, 
the  PERIPHERAL  HALF,  surrounded  by  a  small  amount  of 
protoplasm,  is  thrust  out  of  the  cell.  This  is  the  FIRST 
POLAR  BODY.  Without  rest,  the  remaining  chromosomes 
immediately  undergo  division  again,  and  the  extrusion 
process  is  repeated.  This  is  the  SECOND  POLAR  BODY.  The 
remaining  chromosomes  form  a  new  nucleus  called  the 
GERM-NUCLEUS.  By  this  change,  the  number  of  chromo- 
somes is  reduced  from  twenty-four,  in  the  oocyte,  to  twelve, 
in  the  matured  ovum.  The  first  polar  body  often  divides  into 
two,  and,  as  a  result  of  maturation,  four  cells  are  formed. 
Of  these  four,  the  ovum  is  the  only  one  capable  of  producing 
an  offspring.  The  three  polar  bodies  disintegrate  and  dis- 


206  THE    FEMALE    GENITAL    SYSTEM. 

appear.  This  is  entirely  different  from  the  change  in  the 
testicle.  In  that  oigan,  the  SPERMIOCYTE  gives  rise  to 
FOUR  CELLS,  each  of  which  becomes  a  SPERMIUM,  capable  of 
fertilization. 

As  the  follicle  increases  in  size,  it  approaches  the  tunica 
albuginea,  and  causes  it  to  protrude.  The  stroma  inter- 
vening between  the  ovum  and  the  tunica  gradually  dimin- 
ishes until  merely  the  tunica  albuginea  remains.  As  the 
follicle  increases  and  the  pressure  within  becomes  greater, 
the  tunica  becomes  progressively  thinner,  until  it  is  no 
longer  able  to  withstand  the  pressure.  Then  it  ruptures, 
and  the  liquor  folliculi  and  the  ovum,  surrounded  by  the 
granule  cells,  are  cast  out  of  the  ovary.  The  vessels  of 
the  tunica  vasculosa  rupture,  and  the  follicle  fills  with 
blood.  When  this  occurs,  the  body  is  called  the  CORPUS 
HEMORRHAGICUM.  The  cells  of  the  theca  penetrate  the  clot, 
and  cause  this  to  organize.  In  addition  to  these  cells, 
there  are  certain  other  large  cells  that  possess  a  yellowish 
pigment.  These  are  the  LUTEIN  CELLS,  and  their  function 
is  unknown.  These  are  derived  from  the  theca. 

If  the  ovum  has  not  been  fertilized,  this  body  is  called  a 
CORPUS  LUTEUM  SPURIUM,  which  rapidly  undergoes  atrophy; 
in  a  few  weeks,  it  leaves  a  white  scar  called  the  CORPUS 
ALBICANS.  If  fertilization  has  occurred,  then  the  body 
persists  until  near  the  end  of  pregnancy,  and  is  termed  the 

CORPUS  LUTEUM  VERUM. 

The  CORPUS  LUTEUM  seems  to  be  a  gland  of  short  duration. 
It  seems  to  secrete  a  substance  that  causes  the  second  suc- 
ceeding menstrual  flow,  that  is,  of  the  next  month.  Experi- 
mental study  upon  animals,  in  which  the  follicles  were  de- 
stroyed, showed  an  almost  invariable  absence  of  the  second 
succeeding  period.  The  preceding  flow  was  caused  by  the 
follicle  preceding  the  experiment.  This  secretion  also 
stimulates  the  uterus,  and  aids  the  implantation  of  the 


OVULATION.  207 

ovum  in  the  uterine  mucosa,  providing  fertilization  has 
occurred  (Frankel). 

Of  all  the  follicles  formed,  but  few  are  ever  fertilized.  A 
great  number  atrophy;  in  the  remainder,  MATURATION 
occurs.  Of  these  ova,  there  are  those  which  are  cast  into 
the  abdominal  cavity  and  absorbed  by  the  peritoneum; 
those  which  pass  down  the  genital  tract  and  are  cast 
out,  or  disintegrate,  and  lastly,  those  that  become 
fertilized. 

Ovulation  includes  the  delivery  of  the  ovum  from  the 
follicle  and  its  passage  through  the  genital  apparatus.  In 
the  lower  animals,  in  which  the  young  are  developed  from 
eggs  outside  of  the  body  (OVIPAROUS),  this  process  is 
evinced  by  the  "laying  of  the  egg."  In  the  VIVIPAROUS 
ANIMALS,  or  those  in  which  the  offspring  is  developed 
within  the  mother,  this  process  is  not  accompanied  by  any 
outward  signs  or  manifestations.  In  the  temperate 
climate,  it  begins  at  about  the  twelfth  to  the  fifteenth  year, 
and  continues  until  about  the  forty-fifth  to  the  fiftieth  year. 
At  this  time  ovulation  ceases,  and  fertilization  cannot  occur 
thereafter. 

The  Medulla  consists  of  a  loose  network  formed  by  large, 
coarse  bundles  of  white  fibrous  tissue,  in  which  strands  of 
SMOOTH  MUSCLE  TISSUE  are  found.  These  latter  are  limited 
to  the  medulla.  In  the  meshes  of  the  stroma  are  seen  the 
INTERSTITIAL  CELLS,  which  are  more  numerous  than  in  the 
cortex.  In  this  part  of  the  ovary  are  found  the  large  blood- 
vessel trunks  which  are  very  numerous. 

The  'vessels  enter  the  ovary  at  the  hilus,  and  form  a  large 
number  of  branches  in  the  medulla.  From  these,  smaller 
ones  are  sent  to  the  cortex,  some  passing  to  the  follicles, 
where  they  form  a  dense  surrounding  plexus,  while  others 
pass  to  the  tunica  vasculosa  of  the  tunica  albuginea. 

The  lymphatics  follow  the  vessels  closely. 


208  •         THE    FEMALE   GENITAL    SYSTEM. 

Nerve  fibres  accompany  the  vessels,  and  surround  the 
follicles.  Ganglia  occur  in  the  medulla. 

The  Parovarium,  or  Epoophoron,  lies  near  the  hilus  of 
the  ovary,  and  consists  of  a  number  of  short  vertical  tubules 
united  to  a  single  horizontal  tube.  The  vertical  tubules  are 
short,  and  are  lined  by  low  columnar  cells.  The  horizontal 
tubule  has  a  larger  diameter  than  the  preceding,  and  is 
lined  by  the  same  variety  of  cells.  It  often  lies  deep  in  the 
broad  ligament. 

The  Paroophoron  lies  in  the  broad  ligament,  between 
the  ovary  and  uterus,  and  consists  of  a  number  of  short, 
closed  tubules  lined  by  low  columnar  cells.  The  tubes  re- 
semble the  vertical  tubes  of  the  epoophoron. 

THE  OVIDUCT. 

Although  the  ovary  possesses  no  excretory  apparatus  like 
other  glands,  the  Oviduct,  or  Fallopian  Tube,  acts  as  such. 

The  Fallopian  Tube  consists  of  the  outer  FIMBRIATED 
END,  the  middle,  or  AMPULLA,  and  the  inner  UTERINE  END, 
or  ISTHMUS.  It  has  three  coats,  MUCOUS,  MUSCULAR  and 
FIBROUS. 

The  MUCOUS  coat  consists  of  simple  ciliated  cells  that  lie 
upon  a  basement  membrane  and  tunica  propria.  A  muscu- 
laris  mucosce  is  absent.  The  tunica  propria  is  thrown  into 
longitudinal  folds  that  are  high  in  the  fimbriated  end,  but 
diminish  in  height  as  the  uterus  is  approached.  These 
folds  are  the  VILLI,  which  possess  a  very  narrow  base,  but 
the  part  lying  in  the  lumen  of  the  tube  is  greatly  branched. 
The  tunica  propria  consists  of  white  fibrous  and  yellow 
elastic  tissues,  in  which  diffuse  lymphoid  tissue  is  found. 

The  MUSCULAR  coat  consists  of  involuntary  nonstriated 
muscle  tissue  arranged  in  inner  circular  and  outer  longitudi- 
nal layers.  Near  the  uterine  end,  an  inner  longitudinal 
layer  is  added.  This  corresponds  to  a  muscularis  mucosse. 


OVIDUCT. 


209 


The  FIBROUS  coat  consists  of  white  fibrous  tissue,  and  is 
surrounded  by  peritoneum. 

The  blood-vessels  lie  in  the  deeper  portion  of  the  tunica 
propria.  From  these,  smaller  ones  are  sent  into  the  villi, 
and  into  the  muscular  and  fibrous  coats.  The  vessels  are 
usually  quite  tortuous. 


FIG.  70. — CROSS-SECTION  OF  THE  HUMAN  OVIDUCT. 

a.  Epithelium;  b.  tunica  propria;  c.  villi;  d,  muscular  coat,  inner  circular 
layer;  e.  muscular  coat,  outer  longitudinal  layer;  /.  blood-vessels  in  the 
fibrous  coat;  g.  blood-vessels  in  villus;  h.  fibrous  coat;  k.  epithelium  of 
fimbria;  /.  tunica  propria  of  fimbria. 

The  lymphatics  accompany  the  blood-vessels. 

The  nerves  are  both  myelinated  and  amyelinated.  They 
accompany  the  blood-vessels,  which  they  supply,  and  then 
pass  to  the  mucosa,  where  they  end  in  relation  with  the 
cells. 

14 


210  THE    FEMALE    GENITAL    SYSTEM. 

THE  UTERUS. 

The  Uterus  is  a  flattened,  pear-shaped  organ  that  con- 
sists of  BODY  and  CERVIX.  It  is  an  important  organ,  as 
within  it  develops  the  offspring,  in  viviparous  animals. 
All  parts  consist  of  MUCOUS,  MUSCULAR  and  FIBROUS  coats. 

The  MUCOUS  coat  of  the  body  is  about  i  mm.  in  thickness, 
and  is  composed  of  simple  ciliated  cells,  basement  mem- 
brane and  tunica  propria.  Within  the  latter  are  found  a 
rich  capillary  plexus  and  diffuse  lymphoid  tissue.  The 
surface  is  not  smooth,  but  is  broken  by  the  formation  of 
GLANDS.  These  are  tube-like  depressions  lined  by  the 
simple  ciliated  cells,  and  are  of  the  branched  tubular  -variety. 
They  are  the  UTERINE  GLANDS  and  extend  to  the  muscular 
coat,  but  do  not  penetrate  it.  They  are  often  so  long  that 
When  they  reach  the  muscular  coat,  they  turn  and  extend 
parallel  to  it  for  some  distance. 

The  MUCOSA  of  the  CERVIX  is  a  little  different.  The 
uterine  end  is  lined  by  simple  ciliated  cells,  and  glands  are 
present.  The  -vaginal  end  is  lined  by  stratified  squamous 
cells,  and  gland-like  depressions  are  present.  The  orifices 
often  closed,  causing  them  to  become  distended  with  secre- 
tion. In  this  condition,  they  produce  globular  projections 
called  the  OVULI  NABOTHI.  The  cervical  mucosa  is  thrown 
into  folds  called  the  PLIC.E  PALMATE.  The  vaginal 
portion  of  the  cervix  is  covered  by  stratified  squamous  cells. 

The  MUSCULAR  coat  consists  of  three  layers  of  smooth 
muscle,  inner  longitudinal,  middle  circular  and  outer  longi- 
tudinal. The  inner  longitudinal  probably  represents  an 
hypertrophied  muscularis  mucosoz.  It  is  separated  from  the 
middle  layer  by  a  very  thin  layer  of  connective  tissue. 
This  muscle  layer  is  called  the  STRATUM  MUCOSUM.  The 
middle  layer  is  the  thickest,  and  contains  the  large  vessels. 
It  is  called  the  STRATUM  VASCULARE.  The  outer  longitudi- 


UTERUS. 


211 


nal  layer  lies  just  beneath  the  fibrous  coat,  and  is  often 
called  the  STRATUM  SUPRA VASCULARE. 

In  the  CERVIX,  the  circular  fibres  are  more  pronounced, 
forming  a  dense  band  or  ring. 


•t  mm 


FIG.  71. — RESTING  UTERINE  MUCOSA. 

a.  Mucosa;  b.  epithelium;  c.  gland  tubule  (Stohr's  Histology,  after  Bohm 
and  Davidojf}. 

The  muscle  fibres  average  50  to  60  microns  in  length; 
but,  during  pregnancy,  they  lengthen  to  from  300  to  600 
microns. 

The  FIBROUS,  or  SEROUS,  coat  is  quite  thin.  It  is  com- 
pletely invested  by  peritoneum  in  the  BODY. 


212  THE    FEMALE    GENITAL    SYSTEM. 

Menstruation  is  the  periodic  change  that  occurs  in  the 
uterine  mucosa,  every  twenty-eight  days,  during  the  child- 
bearing  period  (13 th  to  50 th  year).  It  is  divided  into 
stages,  the  HYPERTROPHIC,  DESQUAMATIVE,  REPARATIVE 
and  RESTING  stages. 

During  the  HYPERTROPHIC,  or  CONSTRUCTIVE  stage,  the 
mucosa  increases  to  2  or  3  mm.  in  thickness,  and  the  sur- 
face becomes  irregular.  This  is  due  to  the  increase  in  size 
and  number  of  the  blood-vessels,  and  to  cell  proliferation  in 
the  tunica  propria.  The  glands  become  broader,  deeper 
and  more  tortuous.  This  change  requires  four  to  six  days, 
and  is  succeeded  by  the  DESQUAMATIVE,  or  destructive, 
stage. 

The  DESQUAMATIVE,  or  DESTRUCTIVE,  stage  is  character- 
ized by  the  appearance  of  the  FLOW,  or  FLUX.  It  is  caused 
by  the  diapedesis  of  some  of  the  blood  from  the  capillaries 
of  the  tunica  propria.  The  blood  passes  into  this  layer 
beneath  the  epithelium,  and  cuts  off  the  nutrition  of  the 
overlying  cells,  causing  them  to  undergo  a  fatty  degenera- 
tion. These  cells  then  disintegrate,  exposing  the  vessels, 
which  rupture  and  allow  the  blood  to  pass  into  the  uterine 
cavity.  The  surface  is  thus  left  without  an  epithelial 
covering,  and  the  thickness  of  the  mucosa  becomes  reduced. 
Hoppe-Seyler  states  that  the  average  amount  of  blood  lost 
is  from  26  to  52  cu.  cm.  This  stage,  lasting  three  to  five 
days,  is  followed  by  repair. 

The  REPARATIVE  stage  is  that  in  which  the  mucosa  re- 
turns to  the  normal  condition.  The  hyperemia  disappears, 
and  the  disintegrated  epithelium  is  replaced  by  epithelial 
cells  from  the  glands.  This  stage  requires  about  five  to 
eight  days. 

The  RESTING  stage  constitutes  the  remaining  twelve  to 
fourteen  days  of  the  period.  During  this  stage,  the  uterine 
mucosa  is  quiescent.  Should  fertilization  occur  at  the  time 


VAGINA.  213 

of  the  constructive  stage,  the  other  three  stages  may  not 
take  place. 

The  blood-vessels  are  important.  Two  arteries,  the  uter- 
ine and  ovarian,  supply  the  organ.  The  main  branches  of 
these  arteries  pass  to  the  middle  circular  layer  of  muscle, 
which  plays  the  part  of  submucosa.  Smaller  branches  are 
sent  into  the  mucosa,  and  there  form  plexuses  around  the 
glands.  The  large  trunks  are  very  tortuous,  to  allow  for 
the  increase  in  the  size  of  the  uterus  during  pregnancy. 

The  lymphatics  originate  in  the  mucosa;  these  vessels 
empty  into  a  set  of  larger  vessels  in  the  middle  layer  of  the 
muscular  coat.  From  here  the  vessels  pass  into  the  serous 
coat. 

The  nerve  fibres  are  both  myelinated  and  amyelinated. 
The  former  pass  into  the  mucosa,  some  ending  in  the  epi- 
thelial layer.  The  latter  pass  chiefly  to  the  muscular  tissue. 

THE  VAGINA. 

The  coats  of  the  Vagina  are  the  same  as  those  of  the 
uterus. 

The  MUCOUS  coat  consists  of  stratified  squamous  cells, 
supported  by  basement  membrane  and  tunica  propria.  The 
subepithelial  portion  of  the  tunica  propria  is  papillated. 
The  deeper  portion  contains  many  large  elastic  fibres  and 
considerable  diffuse  lymphoid  tissue.  Occasionally,  some 
simple  tubular  glands  are  met  with,  and  the  lining  cells  are 
of  the  simple  ciliated  variety. 

The  MUSCULAR  coat  varies  in  thickness,  that  nearer  the 
outlet  being  the  thicker.  The  layers  are  not  sharply  sepa- 
rated from  one  another,  but  the  general  direction  is  inner 
circular  and  outer  longitudinal.  The  mucous  and  muscular 
coats  are  thrown  into  folds  that  are  called  RUG^E. 

The  FIBROUS  coat  consists  of  dense  fibrous  tissue,  and 


214 


THE    FEMALE    GENITAL    SYSTEM. 


serves  to  connect, the  vagina  with  the  surrounding  tissues 
and  organs. 

The  larger  vessels  lie  in  the  deeper  portion  of  the  mucosa, 
and  send  branches  into  the  mucosa  and  muscularis.     The 


*?-V 


FIG.  72. — CROSS-SECTION  OF  SEGMENT  OF  HUMAN  VAGINA. 

a.  Stratified  squamous  epithelium;  b.  tunica  propria;  c.  inner  circular  muscle 

fibres;  d.  outer  mixed  muscle  fibres. 

capillaries  of  the  mucosa  pass  chiefly  to  the  papillae.  The 
veins  form  dense  plexuses  beneath  the  fibrous  coat.  Large 
vessels  occur  in  the  lower  part  of  the  mucosa,  causing  it  to 
resemble  cavernous  tissue. 


GENITALIA.  215 

The  lymphatics  follow  the  same  course  as  the  blood- 
vessels. 

The  nerves  are  both  myelinated  and  amyelinated.  Genital 
corpuscles  may  be  found  in  the  mucosa. 

THE  GENITALIA. 

The  VAGINAL  ORIFICE  is  guarded  by  a  delicate  annular,  or 
crescentic  membrane  called  the  Hymen.  This  consists  of 
white  fibrous  tissue  covered  upon  its  external  and  internal 
surfaces  by  stratified  squamous  cells.  Occasionally,  it  is  very 
vascular. 

Just  outside  of  this  fold,  the  primitive  uro-genital  sinus 
spreads  to  form  the  Vestibule  of  the  vagina.  This  is  a 
triangular  space,  with  the  apex  formed  by  the  junction  of 
the  labia  minora,  the  sides  by  these  folds  and  the  base  by 
the  vaginal  orifice.  It  contains  the  opening  of  the  urethra. 
This  space  is  lined  by  stratified  squamous  cells.  In  the 
tunica  propria,  are  found  a  great  many  elastic  fibres  and 
mucous  and  sebaceous  glands,  especially  near  the  opening  of 
the  urethra.  The  lower  portion  of  the  tunica  propria 
contains  so  many  large  venous  channels  that  it  is  practically 

ERECTILE  TISSUE. 

Opening  into  the  vestibule  upon  each  side  is  a  gland,  the 
analog  of  the  gland  of  Cowper  of  the  male.  This  is  the 
GLAND  OF  BARTHOLIN,  which  is  a  compound  racemose  gland, 
and  the  acini  are  lined  by  large,  clear,  mucous  cells.  The 
ducts  are  lined  by  low  columnar  cells. 

Covering  the  vaginal  orifice,  to  a  greater  or  less  extent, 
are  seen  the  Labia  Minora,  or  Nymphae.  These  consist 
of  a  central  mass  of  loose  connective  tissue,  in  which  the 
blood-vessels  are  abundant,  especially  the  veins.  In  the 
tissue  between  the  veins,  smooth  muscle  tissue  exists,  and 
this  with  the  vascularity,  forms  to  ERECTILE  TISSUE.  The 


2l6  .       THE    FEMALE    GENITAL    SYSTEM. 

folds  are  covered  upon  both  sides  by  stratified  squamous 
cells  that  rest  upon  a  papillated  tunica  propn'a.  In  these 
papillae,  capillary  plexuses  are  seen.  Schaccons  glands  are 
numerous,  but  hairs  and  sweat-glands  arc  absent. 

The  Glans  Clitoris  lies  in  the  tissue  formed  by  the  junction 
of  the  labia  minora.  It  is  covered  by  stratified  squamous 
cells.  The  central  part  consists  of  ERECTILE  TISSUE,  and 
many  large  and  small  vascular  papillae  are  present.  Genital 
corpuscles  and  sebaceous  glands  are  found.  The  Glans  is 
covered  by  a  fold  of  skin,  the  PREPUCE,  in  which  the  seba- 
ceous glands  are  quite  numerous. 

The  Labia  Majora  are  merely  folds,  or  pouches  of  skin. 
Their  outer  surfaces  are  covered  by  ordinary  skin.  In  the 
subcutaneous  tissue  are  seen  numerous  vessels,  nerves, 
glands,  bundles  of  smooth  muscle  and  an  abundance  of 
adipose  tissue.  Along  a  median  line,  they  come  in  contact 
with  each  other,  and  the  skin  surface  is  somewhat  modified. 
Here  elastic  and  muscle  tissues  are  abundant,  but  adipose 
tissue  is  wanting.  The  skin  of  the  labia  majora  is  some- 
what darker  than  that  in  the  immediate  neighborhood, 
due  to  the  presence  of  pigment  in  the  epithelial  layers. 
Over  the  pubis,  the  two  labia  meet  and  form  a  prominent 
mass,  the  Mons  Veneris. 

The  various  portions  of  the  female  genital  tract  are  lined 
by  the  following  cells: 

OVIDUCT Simple  ciliated. 

UTERUS. 

BODY       Simple  ciliated. 

CERVIX,  UTERINE  END.     .    .     .  Simple  ciliated. 

VAGINAL  END      .    .     .  Stratified  squamous. 

VAGINA        Stratified  squamous. 

VESTIBULE Stratified  squamous. 

LABIA Stratified  squamous. 


CHAPTER  XV. 


THE  PLACENTA  AND  UMBILICAL  CORD. 

A  description  of  the  formation  of  the  Placenta  and  Cord 
must  be  given  in  order  to  understand  their  structure  at 
term. 

Should  the  ovum  become  fertilized,  it  is  passed  down 
the  oviduct  by  the  ciliated  cells,  as  fertilization  usually 
occurs  in  this  portion  of  the  genital  system.  It  is  sur- 
rounded by  the  zona  pellucida  and  corona,  or  zona  radiata. 
The  mucous  membrane  of  the  uterus  becomes  thickened,  as 
for  menstruation,  and  the  ovum  becomes  lodged,  usually  in 
the  fundus. 

The  mucosa  of  the  uterus  is  divided  into  regions:  that 
immediately  beneath  the  ovum  is  the  PLACENTAL  DECIDUA, 
or  DECIDUA  SEROTINA;  the  ovum  becomes  covered  by  a 
portion  called  the  OVULAR,  or  REFLEX  DECIDUA;  the  re- 
mainder is  the  UTERINE  DECIDUA,  Or  DECIDUA  VERA. 

The  ovum  divides  and  redivides,  and  passes  down 
the  oviduct  toward  the  uterus.  These  cells  form  an 
irregular  mass,  the  MORULA.  The  outer  cells  of  this  mass 
arrange  themselves  beneath  the  zona  pellucida  as  the  SUB- 
ZONAL  ECTODERM,  or  OUTER  CELL  MASS,  while  the  remainder 
constitute  the  INNER  CELL  MASS.  The  entire  structure 
grows  rapidly,  and,  as  a  result,  a  cavity  is  formed  around 
the  inner  mass,  except  at  one  point,  where  it  is  attached  to 
the  subzonal  layer.  The  cavity  is  filled  with  liquid,  under 
pressure.  This  mass  is  called  the  BLASTULA,  or  ONE- 
LAYERED  VESICLE.  The  point  of  attachment  is  called  the 

217 


2l8  THE    PLACENTA   AND    UMBILICAL    CORD. 

EMBRYONIC   AREA.     In  this   condition,   the   ovum    usually 
reaches  the  uterus. 

The  OUTER  MASS,  at  the  point  of  union  with  the  inner  mass, 
becomes  greatly  thickened,  its  upper  portion  being  called 
the  TROPHODERM  (Minot),  and  its  under  portion  the  ecto- 
derm. The  trophoderm  extends  all  around  the  zona 
pellucida,  and  is  closely  applied  to  it.  The  innermost 
cells  of  the  INNER  MASS  then  arrange  themselves  as  a  single 
layer  of  cuboidal  cells  that  extend  into  the  cavity  of  the 
blastula  and  form,  by  meeting,  a  little  vesicle,  the  ento- 


FIG.   73. — DIAGRAM  OF  SUPPOSED  DEVELOPMENT  OF  PRIMATES   (Minot}. 
Tro.   Trophoderm;   EC.   ectoderm;    Mes.    mesoderm;   Ent.   entoderm;   Coe. 

ccelom. 


dermal  'vesicle.  By  this  formation,  the  GASTRULA,  or 
DIPTOBLAST,  in  which  two  distinct  layers,  ectoderm  and 
entoderm,  are  seen,  is  completed.  From  these  two  layers, 
the  'mesoderm  is  derived.  This  constitutes  the  TRIPLOBLAST, 
or  THREE-LAYERED  VESICLE.  The  mesoderm  lies  between 
the  ectoderm  and  entoderm,  and  where  these  layers 
separate,  it  splits  into  two  layers,  one  of  which  accompanies 
the  ectoderm  around  the  triploblast  to  form  the  SOMATO- 
PLEURE,  and  the  other  accompanies  the  entoderm  to  form 
the  SPLANCHNOPLEURE.  The  mass  increases  in  size,  and 
the  trophoderm  in  the  embryonic  area  thickens  greatly. 


TRIPOBLAST.  2IQ 

At  the  same  time,  the  cells  at  the  junction  of  trophoderm 
and  ectoderm  disappear,  leaving  a  space,  the  AMNIOTIC 
CAVITY.  This  cavity  is  now  bounded  by  trophoderm  above 
and  the  combined  ectoderm,  mesoderm  and  entoderm  be- 
neath, these  latter  constituting  the  EMBRYONIC  SHIELD.  At 
the  edges  of  the  cavity,  the  mesoderm  continues  with  the 
trophoderm,  forming  the  PROCHORION. 

At  what  are  to  be  the  cephalad  and  caudad  regions  of 
the  future  embryo,   transverse  depressions  appear  in  the 


FIG.  74. — DIAGRAM  OF  EARLY  DEVELOPMENT  OF  PRIMATES.    Later  Stage  of 

73  (Minot). 
a.   Aminotic  cavity;   b.  ectoderm;   c  and  d.  mesoderm;   e.  entoderm. 

somatopleure  (one  at  each  end) ;  these  are  called  the  head 
and  tail  folds  of  the  amnion,  respectively.  The  lateral  folds 
appear  on  each  side  in  the  same  manner.  All  these  grooves 
deepen,  and  the  somatopleure  extends  ventrally  from  all 
directions  (less  from  caudad)  to  form  the  body-wall;  its  re- 
turn folds  pass  dor  sally  over  the  embryo  to  unite,  forming 
an  inner  membrane  next  to  the  embryo,  the  true  amnion, 
and  an  outer  above  the  embryo,  the  FALSE  AMNION,  or  PRIMI- 
TIVE CHORION.  The  prochorion  consists  of  trophoderm 
(ectoderm  called  also  the  placentoblast)  and  mesoderm;  the 
amnion,  of  mesoderm  and  ectoderm,  and  the  body-wall  of 


220  THE    PLACENTA  AND    UMBILICAL   CORD. 

ectoderm  and  mesoderm,  respectively.  At  all  points,  like 
layers  are  opposed  to  like  layers.  In  the  formation  of  the 
body-wall  and  amnion,  the  SPLANCHNOPLEURE  has  been 
pushed  before  the  somatopleure  to  form  a  tube  within  the 
body,  the  GUT-TRACT  and  a  sac  outside,  the  YOLK  SAC  and 

VITELLINE  DUCT. 

In  the  formation  of  the  amnion,  the  embryo  loses  its 
connection  with  the  chorion  at  all  points,  except  caudally, 
where  the  mesoderm  and  ectoderm  of  the  two  are  continuous, 
forming  the  BELLY-STALK. 

By  this  time,  the  ovum  has  become  lodged  in  the  uterine 
mucosa.  This  process  is  accomplished  by  the  aid  of  the 
trophodermal  cells,  that  have  the  power  of  phagocytosis 
(destruction  of  tissue)  and  erode  the  superficial  tissues  of  the 
mucosa,  forming  a  cavity  into  which  the  ovum  sinks.  The 
epithelium  of  the  uterus  is  lost  in  this  region  and  also  in  the 
glands  and  the  superficial  vessels  are  exposed.  The  tropho- 
derm,  or  placentoblast  becomes  thrown  into  little  proc- 
esses, or  mlli  (present  as  early  as  the  fifth  day,  Peters), 
due  to  actual  growth  and  the  disappearance  of  cells  in  the 
trophoderma'  layer.  As  a  result,  there  are  formed  a  series 
of  intercommunicating  spaces,  the  trophodermal  lacuna. 
The  villi  are  composed  of  trophoderm  and  mesoderm.  When 
the  vessels  of  the  mucosa  are  exposed,  they  rupture  into  the 
glandular  spaces,  and  from  these,  the  maternal  blood  gains 
access  to  the  trophodermal  lacuna,  or  spaces.  Thus  does 
the  embryo  receive  nourishment  from  the  mother,  before 
the  umbilical  vessels  are  present.  The  area  of  the  ovum 
left  uncovered  when  the  ovum  becomes  lodged,  is  covered 
by  mucosa  that  is  reflected  from  the  lining  at  the  sides  of 
the  ovum.  This  is,  therefore,  called  DECIDUA  REFLEXA, 

Or  OVULAR  DECIDUA. 

We  must  remember  that  the  BELLY-STALK  connects 
the  embryo  with  the  prochorion.  This  belly-stalk  is  of 


OVIPAROUS.  221 

importance,  because  it  represents  that  part  of  the 
embryonic  disc  that  does  not  lose  connection  with  the 
prochorion  during  the  formation  of  the  body-wall  and 
gut-tract.  Into  the  belly-stalk  the  allantoic  evagination 
of  the  gut-tract  extends  for  a  short  distance,  while  the  allan- 
toic vessels  pass  along  the  entire  extent  of  the  stalk  to  the 
forming  chorion.  With  the  passage  of  the  allantoic  vessels 


FIG.  75. — DIAGRAM  OF  EARLY  DEVELOPMENT  OF  PRIMATES.     Later  than 

FIG.  74.  (Minot). 

a.  Amnion;  b.  chorion;  c.  embryo;  d.  yolk-sac;  e.  body-stalk;  /.  allantois; 
g.  entodermal  cavity  of  embryo;  h.  entoderm;  i.  chorionic  villi. 

to  vascularize  the  chorion,  the  belly-stalk  becomes  the  so- 
called  extra- embryonic  portion  of  the  allantois.  In  some 
animals,  the  OVIPAROUS,  the  allantois  loses  connection 
with  the  belly-stalk,  and  is  free.  It  remains  as  a  dilated 
sac,  and  serves  as  a  receptacle  for  urine.  In  the  viviparous 
animals,  it  remains  connected  with  the  belly-stalk,  and  is 
said  to  connect  the  embryo  with  the  uterus,  becoming  the 


222  THE    PLACENTA  AND    UMBILICAL   CORD. 

organ  of  nutrition  and  respiration.  As  a  matter  of  fact, 
it  seems  to  be  the  belly-stalk  that  forms  the  link  between 
fetus  and  chorion;  the  chorion  becomes  the  fetal  portion 
of  the  placenta,  while  the  belly-stalk  becomes  the  umbilical 
cord  by  the  addition  of  the  vessels.  It  would  seem  that 
the  allantois  proper  has  nothing  to  do  with  the  formation 
of  the  placenta  and  cord  in  the  higher  types.  In  this 
mesoderm,  four  main  vessels  develop,  two  arteries  and  two 
veins.  Later  but  one  vein  is  found,  due  either  to  a  fusion 
of  the  two  veins,  or  more  probably  to  the  atrophy  of  the  right 
vein.  The  two  veins  enter  the  body  and  proceed  toward  the 
heart,  while  the  other  two  vessels  pass  into  the  body,  and 
connect  with  the  aorta.  The  distal  ends  of  all  the  vessels 
pass  into  the  chorion,  and  divide  to  ramify  all  the  villi. 
These  villi  are  still  covered  by  the  trophoderm,  consisting 
usually  of  two  layers.  Of  these,  the  outer  becomes  con- 
verted into  a  thin  layer  of  protoplasm,  in  which  the  original 
nuclei  remain  and  the  cell-boundaries  are  lost.  This  pro- 
toplasm constitutes  the  SYNCYTIUM. 

The  villi  do  not  long  remain  simple,  but  branch  and  re- 
branch; the  vessels  follow  these  branches,  and  penetrate 
to  the  very  ends.  Some  of  the  villi  enter  the  uterine 
glands,  in  which  the  epithelium  becomes  denuded  by 
about  the  sixth  week,  and  the  surface  cells  by  the  fourth 
week,  and  are  the  floating  villi;  others  become  attached,  and 
form  the  fixed  villi.  When  the  epithelium  of  the  uterus 
is  lost,  the  engorged  superficial  capillaries  of  the  placental 
decidua  become  connected  with  the  glands,  and  the  blood 
enters  these,  and  then  the  trophodermal  spaces.  These 
channels  are  the  later  intervillous  spaces.  From  these 
cavities,  the  blood  is  returned  to  the  venous  channels  of 
the  mucosa,  but  no  direct  connection  is  established  between 
the  fetus  and  the  mother. 

These  villi  are  very  abundant,  and  may  be  scattered  all 


CHORION. 


223 


over  te  ovum  or  be  limited  to  the  equator  of  the  mass- 
Up  to  his  time,  all  are  equal  in  size.  Soon  a  difference  is 
noted  i  size,  those  at  the  place  of  attachment  of  the  ovum 
increar  in  number  and  size,  forming^the  chorionf rondo  sum, 


FIG.   ;  i  \<;KAMMATIC    OUTLINE   OF   A  DORSO- VENTRAL  SECTION 

I:RUS  CONTAINING  AN  EMBRYO  OF  ABOUT  FIVE  WEEKS. 

a.  Veni  a       dorsal   surface;  g.  outer  limit  of  decidua;  s,  s.  limits  of   the 

placen  j   decidua;  ch.  chorion,  within  which  is  the  embryo  enclosed  by 

and  attached  to  the  chorion  by  the  umbilical  cord;  from 

the  coi  hangs  the  pedunculated  yolk-sac;  r,  r.  ovular  decidua  (Minot). 

while  th<  remainder  disappear  and  constitute  the  chorion 

latter  do  not  become  vascularized. 

At  abot  the  fifth  month,  a  villus  has  the  following  ap- 
pearance   Of  the  trophodermal  cells,  the  outer  do  not  re- 


224  THE    PLACENTA   AND    UMBILICAL   CORD. 

main  large,  distinct  elements,  but  become  flattened,  and 
represent  a  mere  layer  of  nucleated  protoplasm  that  covers 
the  villi;  this  is  the  syncytium,  and  it  is  the  covering  of  the 
embryonic  connective  tissue  that  constitutes  the  core  of  the 
villi  and  supports  the  vessels.  In  the  inner  layer,  the  cells 
remain  distinctly  outlined,  and  persist  for  a  short  time  as 
the  cell-layer  of  Langhans.  From  the  fifth  month  on,  they 
disappear  so  that  ultimately  only  the  syncytium  remains. 
Here  and  there  on  the  villi  are  seen  groups  of  cells  that  rep- 
resent collections  of  syncytial  cells,  the  cell  knots.  These, 
like  the  other  syncytium,  contain  nuclei  that  are  small, 
but  stain  deeply.  The  protoplasm  responds  well  to  the  acid 
stains.  The  Langhans  cells,  however,  contain  large  nuclei, 
but  neither  these  nor  the  protoplasm  respond  well  to  stains. 

After  the  third  month,  the  number  of  villi  that  become 
attached  to  the  mucosa  rapidly  increases,  so  that  after  that 
time  the  fetal  and  maternal  portions  become  more  and 
more  fixed  to  each  other. 

This  is  the  beginning  of  the  formation  of  the  placenta 
as  it  is  seen  at  birth.  The  villi  branch  repeatedly,  and 
the  whole  structure  grows  rapidly,  causing  the  child  to  do 
the  same.  Any  disturbance  that  will  retard  the  growth  of 
the  placenta  will  also  retard  the  growth  of  the  fetus  in  greater 
proportion.  The  difference  between  the  placenta  at  the 
fourth  or  fifth  month  and  at  birth  is  merely  in  size.  This 
is  due  to  the  increase  in  number  and  branches  of  the  villi. 
The  villi  are  separated  into  groups  by  connective-tissue 
septa  that  are  derived  from  the  uterine  tunica  propria. 
These  are  the  placental  septa. 

At  birth  the  Placenta  is  a  flesh-like,  saucer-shaped  mass, 
the  attached  surface  of  which  is  divided  into  lobes,  or 
cotyledons.  The  fetal  surface  is  covered  by  the  amnion,  a 
continuation  of  the  sac  in  which  the  fetus  lies,  and  shows 
the  vessels  as  they  enter  and  leave  the  organ;  the  opposite 


PLACENTA. 


225 


surface  is  divided  into  lobes,  or  cotyledons,  covered  by  the 
decidua  serotina.     The  weight  of   the  placenta  is  about 


si 


xl3 


FIG.  77. — HUMAN  PLACENTA  AT  TERM. 

A.  Vertical  section  at  margin;  D.  decidua;  Cho.  chorion;  Fib.  fibrin;  Vi. 
placental  villi;  Si.  marginal  sinus;  vi.  aborted  extra-placental  villi; 
b.  decidual  tissue.  B.  Portion  of  decidual  tissue  at  b  highly  magnified; 
v.  blood-vessels;  d.  decidual  cells  with  one  nucleus;  d'.  multinucleated 
decidual  cells  (Minoi). 

one-sixth  that  of  the  child.     It  consists  of  two  portions, 
the  fetal  and  maternal. 

This  organ  consists  of  a  fleshy  mass  lying  between  two 


226  THE    PLACENTA  AND    UMBILICAL   CORD. 

membranes.  Upon  the  fetal  surface,  we  find  the  AMNION 
and  CHORION.  The  AMNION  consists  of  a  single  layer  of 
cuboidal  epithelial  cells  that  rest  upon  the  mesodermal 
tissue.  These  epithelial  cells  possess  prominent,  deeply- 
staining  nuclei,  but  the  protoplasm  does  not  react  well  to 
the  stain.  The  mesodermal  tissue  is  somewhat  fibrillar, 
and  few  cells  are  present.  It  is  avascular. 

The  CHORION  is  composed  of  mesodermal  tissue  in  which 
the  fibrils  are  more  or  less  distinct.  This  mesoderm  is 
covered  by  trophodermal  (ectodermal)  cells  that  later  be- 
come the  syncytium.  From  the  side  opposite  to  the  amnion 
are  seen  projections.  These  may  vary  from  small  simple 
villi  to  those  resembling  a  tree  possessing  an  enormous 
number  of  twigs.  Along  this  surface  of  the  chorion,  may 
be  seen  masses  of  a  fibrillar  substance  that  are  called 
canalized  fibrin.  The  bulk  of  the  placenta  consists  of  villi. 
These  form  a  reddish  spongy  mass,  divided  into  masses 
called  cotyledons.  The  main  stems  contain  two  or  more 
vessels  surrounded  by  mesodermal  tissue.  Peripherally, 
each  villus  is  covered  by  a  thin  layer  of  nucleated  proto- 
plasm, the  syncytium.  The  small  twigs  consist  of  a  core 
of  mucous  connective  tissue  supporting  several  small  capil- 
laries. The  syncytium  surrounds  each  twig.  In  places 
are  seen  collections  of  nuclei  representing  the  cell-knots. 
The  cavities  between  the  villi  are  the  intermllous  spaces  con- 
taining the  maternal  blood  and,  at  times,  canalized  fibrin. 

From  this,  it  is  readily  seen  that  the  fetal  and  maternal 
blood  currents  do  not  intermingle.  They  are  separated  from 
each  other,  the  endothelium  of  the  fetal  capillaries  on  the 
one  hand,  and  the  syncytium  of  the  villi  on  the  other. 

The  maternal  side  of  the  placenta  is  covered   by   the 

DECIDUA    SEROTINA,     or     the     STRATUM     COMPACTUM     of     the 

mucosa.  It  is  less  than  a  millimeter  thick,  and  possesses  a 
number  of  short  oblique  channels.  These  are  the  remains 


MEMBRANES.  227 

of  the  uterine  glands;  they  now  represent  blood  sinuses, 
which  contain  maternal  blood. 

The  serotina  extends  into  the  fetal  portion  as  the  placen- 
tal  septa,  and  divides  it  into  the  cotyledons.  At  the  edge 
of  the  placenta,  it  becomes  attached  to  the  chorion,  and 
continues  as  the  DECIDUA  VERA.  At  this  junction  there  is 
a  considerable  space  that  extends  all  around  the  edge  of  the 
placenta.  This  is  the  marginal  sinus,  and  is  prominent  be- 
cause few  or  no  villi  have  developed  here. 

The  MEMBRANES  consist  of  the  AMNION  and  the  uterine 
lining,  or  the  STRATUM  COMPACTUM.  The  latter  is  thin,  and 
contains  neither  glands  nor  epithelium.  When  the  fetus 
increases  in  size  and  causes  a  dilatation  of  the  uterus,  the 
amniotic  sac  is  forced  against  the  uterine  lining,  and 
causes  an  atrophy  of  the  glands  and  cells  of  the  stratum 
compactum.  As  a  result,  a  mere  fibrinous  membrane, 
that  has  a  loose  connection  with  the  amnion,  is  produced, 
due  entirely  to  pressure. 

Fossati,  by  means  of  the  Golgi  method,  found  a  peculiar 
network  of  fibres  surrounding  the  blood-vessels  of  the 
placenta  and  umbilical  cord;  this  network  also  seemed  to 
come  into  relation  with  the  epithelium.  He  considered 
this  network  nerve  tissue. 

The  Umbilical  Cord  is  the  connecting  link  between  the 
fetus  and  the  placenta,  and  represents  the  early  belly- 
stalk.  It  is  surrounded  by  one  or  more  layers  of  cuboidal 
epithelial  cells,  continuous  on  the  one  hand  with  epithelium 
of  the  amnion,  and  on  the  other  with  the  ectodermal  cells 
of  the  body,  supported  by  a  little  subepithelial  fibrous 
tissue.  Within  this  covering  is  the  peculiar  tissue  called 
WHARTON'S  JELLY.  This  is  embryonic  connective  tissue  in 
which  the  cells  are  chiefly  spindle-shaped;  some  round  and 
stellate  cells,  however,  are  seen.  The  intercellular  sub- 
stance is  semi-solid,  and  takes  a  peculiar  homogeneous  stain. 


228  THE   PLACENTA  AND    UMBILICAL   CORD. 

During  the  early  months  of  pregnancy,  the  intercellular 
substance  contains  a  great  deal  of  water,  and  the  cellular 
elements  are  few.  At  the  end  of  pregnancy  the  intercellu- 
lar substance  is  more  or  less  fibrillar,  though  the  semi-solid 
portion  predominates.  At  this  time  the  cells  are  mostly 
of  the  stellate  type,  but  not  numerous.  At  the  body  end, 
occasionally,  traces  of  allantoic  cavity  and  yolk  sac  are 
found. 

The  VESSELS  contained  are  the  single  UMBILICAL  VEIN  and 
two  UMBILICAL  ARTERIES.     These  are  thick-walled  and  well- 


FIG.  78. — CROSS-SECTION  OF  HUMAN  UMBILICAL  CORD  (Minot). 
A,  A'.     Umbilical  arteries;  V.  umbilical  vein;  Y.  remains  of  allantois. 

developed,  and  the  muscle  fibres  run  both  circularly  and 
longitudinally.  The  wall  of  the  arteries  is  thicker  than  that 
of  the  vein.  The  insertion  of  the  cord  into  the  placenta  is 
usually  eccentric,  and  at  this  point  the  vessels  branch 
rapidly  and  spread  out  in  all  directions. 

The  circulation  of  the  placenta  is  a  closed  one.  The  blood 
is  carried  from  the  iliac  arteries  to  the  umbilicus  through  the 
hypogastric  arteries,  which  continue  in  the  cord  as  the  um- 
bilical arteries.  These  branch  to  follow  the  villi  and  ulti- 
mately terminate  in  tufts  of  capillaries  in  the  terminal 
villous  twigs.  The  blood  at  this  point  receives  the  oxygen 
and  nutritive  matter  from  the  maternal  blood  that  circulates 


FETAL    CIRCULATION.  22Q 

in  the  intervillous  spaces  in  which  the  villi  lie.  There  is 
no  direct  communication  between  the  feted  and  maternal  blood, 
for  they  are  separated  from  each  other  by  the  endothelium 
of  the  capillaries  and  the  syncytium  covering  the  villi.  As 
the  oxygen  and  nutritious  substances  pass  into  the  fetal 
blood,  the  effete  matter  and  gases  pass  out  into  the  maternal 
blood.  The  principle  is  the  same  as  in  the  lung,  where  the 
blood  is  oxygenated.  Red  cells  never  pass  from  one  system 
to  another,  but  leukocytes  that  have  the  power  of  ameboid 
motion  may.  The  blood  is  collected  by  the  radicals  of  the 
umbilical  -vein  and  carried  into  the  body  to  the  under  sur 
face  of  the  liver,  where  a  portion  enters  the  portal  vein 
through  the  continuation  of  the  umbilical  vein,  is  dis- 
tributed to  the  liver  and  collected  by  the  hepatic  veins  and 
emptied  into  the  postcava;  the  remainder  is  carried  to  the 
postcava  (inferior  vena  cava)  by  the  ductus  venosus.  The 
blood  passes  to  the  right  auricle,  then  through  {.he  foramen 
ovale  to  the  left  auricle,  from  which  it  passes,  through  the 
auriculo-ventricular  orifice,  into  the  left  ventricle.  The 
blood  then  passes  into  the  aorta  chiefly  to  the  upper  ex- 
tremities and  head,  is  collected  by  the  radicals  of  the 
precava  (superior  vena  cava),  and  emptied  into  the  right 
auricle.  From  this  chamber  it  passes  through  the  auric- 
ulo-ventricular orifice  into  the  right  ventricle,  from 
which  it  passes  into  the  pulmonary  artery  toward  the 
lungs.  As  these  organs  do  not  functionate  at  this  time, 
most  of  the  blood  is  sent  to  the  aorta  through  the 
ductus  arteriosus.  The  blood  then  passes  toward  the 
lower  extremities,  and,  as  it  reaches  the  internal  iliac 
arteries,  most  of  it  is  sent  to  the  placenta  through  the 
arterial  trunks,  which  inside  of  the  body  are  called  the 
hypogastric  arteries,  and  in  the  cord  the  umbilical  arteries. 


CHAPTER  XVI. 


THE  SKIN  AND  ITS  APPENDAGES. 

The  Skin  covers  the  external  surface  of  the  body  and  is 
its  most  extensive  organ.  It  consists  of  two  portions,  the 
Epidermis,  or  Cuticle,  and  the  Cutis  Vera,  or  Corium. 

The  Epidermis  is  the  epithelial  portion  of  which  the  appen- 
dages are  modifications.  It  consists  of  stratified  squamous 
cells,  which,  over  the  general  body  surface,  are  divisible  into 
two  layers,  STRATUM  MALPIGHII  and  STRATUM  CORNEUM. 

The  STRATUM  MALPIGHII,  or  RETE  MUCOSUM,  is  composed 
of  a  number  of  layers  of  cells.  The  basal  part  consists  of 
columnar  elements,  and  is  called  the  GENETIC  LAYER.  The 
cells  stain  deeply,  and  under  certain  conditions  show  pig- 
ment granules.  The  layer  is  uneven  in  its  course,  as  it 
conforms  to  the  waves  of  the  corium.  The  upper  cells  of 
the  stratum  Malpighii  are  large  polyhedral  elements  that  do 
not  touch  one  another,  but  are  separated  by  intercellular 
spaces.  Each  cell  is  provided  with  a  number  of  delicate 
spines,  or  prickles,  that  meet  those  of  other  cells,  and  thus 
prevent  the  cell-bodies  from  coming  into  contact  with  one 
another.  These  are  the  PRICKLE  CELLS.  As  the  upper  part 
of  this  stratum  is  approached,  the  cells  become  flattened 
and  have  an  even  course. 

The  STRATUM  CORNEUM  ordinarily  forms  a  thin  layer. 
Its  cells  are  very  thin  and  scale-like  and  usually  possess  no 
nuclei.  They  are  derived  from  the  cells  beneath,  but  differ 
from  them  in  consisting  of  keratin  that  gives  them  their 
hard  and  horny  characteristic.  These  cells  are  constantly 
cast  off,  and  the  cells  below  increase  to  replace  them.  Be- 

230 


DERMA.  231 

tween  these  two  layers  an  irregular  STRATUM  GRANULOSUM 
is  often  seen. 

In  certain  parts  of  the  body,  sole  and  palm,  the  STRATUM 
GRANULOSUM  and  another,  the  STRATUM  LUCIDUM,  are  well 
developed. 

The  STRATUM  GRANULOSUM  lies  external  to  the  stratum 
Malpighii,  and  is  composed  of  two  or  three  layers  of  flattened, 
spindle-shaped  cells  that  contain  a  deeply-staining  nucleus 
and  coarsely  granular  protoplasm.  The  granules  are 
keratohyalin  that  later  form  the  horny  matter  of  the 
stratum  corneum.  These  granules  are  quite  large  and 
prominent,  and  respond  well  to  hematoxylin.  They  seem 
to  be  modified  protoplasm,  but  some  hold  that  they 
represent  products  of  the  degenerating  nucleus. 

The  STRATUM  LUCIDUM  lies  external  to  the  stratum 
granulosum,  and  separates  this  from  the  stratum  corneum. 
It  forms  a  narrow,  glistening  band  of  cells,  two  or  three 
layers  broad,  in  which  the  keratohyalin  granules  have  fused 
to  form  a  homogeneous  substance,  called  eleidin.  This 
substance  reacts  well  to  eosin.  The  nuclei  are  not  promi- 
nent nor  are  the  cell-bodies  distinct. 

The  Derma,  True  Skin,  or  Cutis  Vera,  is  composed  of 
connective  tissue  arranged  in  two  or  more  less  distinctly 
separated  layers.  These  are  the  STRATUM  PAPILLARE,  or 
outer,  and  the  STRATUM  RETICULARE,  or  inner. 

The  STRATUM  PAPILLARE  consists  of  delicate  bundles  of 
small  white  fibrils  forming  a  close  network  with  elastic 
fibres. 

The  upper  portion  of  this  stratum  is  thrown  into  small 
waves  called  the  papilla,  to  which  the  stratum  Malpighii 
conforms.  Over  the  general  skin  surface,  these  papillae  do 
not  extend  through  the  stratum  Malpighii,  but  in  the  palmar 
and  plantar  regions  they  are  visible  externally,  and  cause 
the  peculiar  markings  seen  in  these  areas.  These  papillae 


232 


THE    SKIN  AND   ITS   APPENDAGES. 


are  important,  as  they  contain  either  capillary  plexuses  or 
special  sensor  nerve  beginnings.  The  lower  portion  of  the 
papillare  consists  of  a  looser  network,  in  which  the  vessels 


FIG.  79. — CROSS-SECTION  OF  SKIN  OF  SOLE  OF  FOOT. 

a.  Stratum  corneum;  b.  stratum  lucidum;  c.  stratum  granulosum;  d.  stratum 
Malpighii;  e.  derma;  /.  panniculus  adiposis;  g.  duct  of  sweat  gland; 
h.  prickle  cells;  i.  genetic  layer;  k.  cross-section  of  a  smooth  muscle 
fibre;  /.  duct  of  sweat  gland;  m.  Pacinian  body;  n.  secretory  portion  of 
sweat  gland;  o.  muscle  of  tubule;  p.  blood-vessel;  q.  adipose  tissue. 

form  plexuses  parallel  with  the  surface.     It  gradually  passes 
into  the  STRATUM  RETICULARE. 

The  STRATUM  RETICULARE  is  not  distinctly  separable  from 
the  preceding.     It  is  composed  of  larger  bundles  of  coarser 


DERMA.  233 

fibrils  of  white  fibrous  tissue,  and  contains  some  yellow 
elastic  tissue,  as  will  be  seen  below.  Here  are  found  the 
larger  blood-vessels  and  the  appendages  and  special  sensor 
nerve  beginnings.  In  the  corium  of  the  scrotum,  penis 
and  nipple,  smooth  muscle  fibres  are  found.  When  these 
bundles  contract,  "goose-flesh"  is  produced. 

The  elastica  is  often  separated  into  layers,  of  which  there 
are  four,  the  subepithelial,  papillary,  reticular  and  sub- 
cutaneous elastic  layers. 

Beneath  the  stratum  reticulare  is  usually  a  layer  of 
adipose  tissue  that  separates  the  skin  from  the  fascia. 
This  is  the  PANNICULUS  ADIPOSUS,  and  it  varies  in  thickness 
in  the  different  regions. 

The  color  of  the  skin  is  due  to  the  presence  of  pigment 
granules  in  the  lower  layers  of  the  stratum  Malpighii.  Such 
granules  have  been  found  even  in  the  corium.  In  the  white 
races,  this  pigmentation  is  limited  to  the  nipple  and  genital 
region.  Whether  the  pigment  is  due  to  the  vital  activity 
of  the  cells,  or  whether  it  is  brought  here  and  deposited,  is 
not  definitely  settled.  The  former  seems  to  be  the  origin 
of  that  of  the  retinal  cells  and  probably  of  that  of  the  skin. 

The  skin  is  the  protective  organ,  and  varies  in  thickness  in 
the  different  regions.  It  is  thinner  on  the  less  exposed  sur- 
faces, as  the  inner  surfaces  of  the  thighs  and  arms,  and 
thicker  on  the  exposed  regions,  as  back,  sole  and  palm. 

Upon  the  palmar  and  plantar  surfaces  the  epithelium  is 
thrown  into  ridges.  These  are  arranged  in  definite  patterns 
characteristic  of  each  individual.  Recorded  impressions 
of  these  surfaces  have  been  used  as  means  of  identification 
for  various  purposes.  Wilder  considers  the  plantar  patterns 
more  characteristic  than  the  palmar  patterns. 

The  blood-vessels  of  the  skin  vary  in  size  and  number, 
according  to  the  location;  in  the  gluteal,  plantar  and  palmar 
regions,  they  are  greater,  while  in  the  most  movable  parts 


234  THE    SKIN  AND   ITS   APPENDAGES. 

they  are  most  branched.  The  larger  trunks  lie  in  the 
reticulare,  parallel  to  the  surface,  and  form  a  capillary  plexus 
in  the  papillare.  From  this  plexus,  capillary  tufts  enter  the 
various  papillae.  The  latter  vessels  continue  as  venous  cap- 
illaries, that  form  a  plexus  just  beneath  the  papillae.  This 
empties  into  another  in  the  lower  portion  of  the  derma  that 
communicates  with  a  subdermal  plexus;  the  latter  lies  be- 
tween the  derma  and  the  panniculus  adiposus,  and  its 
vessels  possess  valves. 

The  long  nerve  trunks  are  found  in  the  reticulare,  and 
from  these  branches  form  a  subpapillary  plexus.  Myelin- 
ated  fibres  extend  toward  the  surface,  and  form  the  special 
beginnings. 

The  sensor  organs  are  very  numerous  in  the  skin.  These 
comprise  the  free  beginnings,  or  those  in  which  the  naked 
axis  cylinder  pierce  the  epithelial  layer,  branch  and  send 
these  divisions  between  epithelial  cells.  The  higher  forms 
of  beginnings  comprise  tactile  corpuscles  of  Meissner,  most 
numerous  in  the  palmar  and  plantar  skin  of  the  ringers 
and  toes;  bulbs  of  the  conjunctiva  and  genitalia;  Pacinian 
bodies  especially  in  the  palms  and  soles;  and  the  organs  of 
Ruffini,  resembling  the  neuro -muscular  beginnings.  For  a 
detailed  description,  see  Nerve  Tissue  (p.  90).  In  addition, 
there  is  the  usual  nerve  supply  to  the  blood-vessels. 

The  lymphatics  of  the  skin  consist  of  superficial,  or  papil- 
lary plexus,  which  receives  the  lymph  from  the  spaces  in 
the  papillae,  and  a  deeper,  or  subcutaneous  plexus  that  con- 
sists of  larger  trunks,  that  anastomose  with  the  above,  and 
communicate  with  the  special  plexuses  of  the  appendages. 

THE  APPENDAGES. 

The  Appendages  of  the  skin  are  the  Hairs,  Nails,  Se- 
baceous, Sweat  and  Mammary  Glands.  These  are  all  de- 
rived from  the  epidermis. 


HAIRS. 

THE  HAIRS. 


235 


The  Hairs  are  protective  organs  limited  to  certain  por- 
tions of  the  body.  Each  consists  of  a  ROOT,  that  portion 
within  the  skin,  and  a  SHAFT,  that  part  seen  above  the 
surface. 


FIG.  80. — FROM  A  SECTION  OF  SCALP  (Stohr's  Histology). 

i.  Hair-shaft;  2.  hair-root;  3.  sebaceous  gland;  4.  arrector  pili  muscle;  5. 

root  sheaths;  6.  follicular  sheath;  7.  hair-bulb;  8.  papilla;  9.  fat  cells. 


The  ROOT  is  somewhat  flask-shaped,  the  lower  end  being 
enlarged  to  form  the  HAIR-BULB.  This,  on  its  under 
surface,  is  indented  and  invaginated  by  a  little  mass  of 
connective  tissue,  the  HAIR  PAPILLA,  that  contains  a  small 
tuft  of  capillaries,  upon  which  the  nourishment  of  the  hair 
solely  depends.  The  root  is  surrounded  by  a  condensation 


236  THE    SKIN   AND    ITS   APPENDAGES. 

of  the  derma,  in  which  the  connective  tissue  bundles  are 
arranged  into  two  layers. 

In  the  outer,  the  fibres  have  a  longitudinal  course,  while 
in  the  inner,  they  run  circularly.  Within  this  circular  layer 
is  a  prominent  homogeneous  band,  the  glassy  membrane. 
This  represents  a  greatly  hypertrophied  basement  mem- 
brane. These  layers  constitute  the  FOLLICULAR  SHEATH. 
Internal  to  it  are  found  the  epithelial  cells,  which  are 
continuous  with  the  epidermis.  These  are  arranged  into 
layers  that  are  the  ROOT  SHEATHS,  of  which  there  are  two, 
OUTER  and  INNER. 

The  OUTER  ROOT  SHEATH  is  the  direct  cont'nuation  of  the 
stratum  Malpigh.'i.  These  cells  are  the  same  as  elsewhere, 
and  continue  to  the  bottom  of  the  root,  where  they  blend 
with  those  of  the  inner  root  sheath.  Throughout  the 
greater  part  of  the  follicle,  this  layer  consists  of  several 
rows  of  cells.  Toward  the  bulb,  it  gradually  becomes 
reduced  to  a  single  layer. 

The  INNER  ROOT  SHEATH  begins  at  the  lower  edge  of  the 
orifice  of  the  sebaceous  gland  that  opens  into  the  hair 
follicle.  Above  the  duct  it  is  replaced  by  the  stratum 
corneum.  This  sheath  consists  of  two  portions,  the  outer 
of  which  is  called  the  LAYER  OF  HENLE.  This  lies  next  to 
the  outer  root  sheath,  and  is  composed  of  a  single  layer  of 
flattened  cells.  Within  this  layer  is  the  sheath,  or  LAYER  OF 
HUXLEY,  which  consists  of  two  or  three  layers  of  large 
irregular  cells.  In  the  bulb  all  of  these  layers,  including 
the  outer  root  sheath,  are  inseparable,  and  gradually  pass 
over  into  the  hair  itself. 

The  Hair  occupies  the  central  portion  of  the  follicle,  and 
is  composed  of  three  parts,  CUTICLE,  CORTEX  and  MEDULLA. 

The  CUTICLE  is  composed  of  a  single  layer  of  irregular, 
nonnucleated  scales.  These  are  very  thin  and  overlap. 
Within  the  follicle  they  lie  closely  applied  to  the  layer  of 


-NAILS.  237 

Huxley.  The  CORTEX  consists  of  a  great  many  layers  of 
long,  spindle-shaped  elements.  The  nuclei  are  rod-shaped. 
The  MEDULLA,  when  present,  is  composed  of  several  rows  of 
cuboidal  cells  that  do  not  extend  the  length  of  the  hair. 
They  contain  granules  of  keratohyalin,  and  frequently 
have  a  dark  appearance;  this  is  due  to  the  presence  of  small 
air-bubbles. 

The  heaviest  hairs  are  found  on  the  scalp  and  pubis,  in 
the  axilla,  and  upon  the  face  of  males.  Delicate  hairs  oc- 
cur all  over  the  body  surface,  and  these  are  like  the  LANUGO 
HAIRS  of  the  fetus. 

The  color  of  the  hair  is  due  to  pigment  granules  in  the 
cortex.  These  cells  may  even  contain  pigment  in  solution. 
Diffuse  pigment  is  abundant  in  dark  and  red  hairs,  but  ab- 
sent in  white. 

Opening  into  the  hair  follicles  are  the  SEBACEOUS  GLANDS. 
This  is  usually  upon  the  side  toward  which  the  hair  leans, 
and  here  is  also  seen  the  muscle  of  the  hair  follicle,  the 
ARRECTOR  PiLi  muscle.  This  is  smooth  muscle,  and  is  at- 
tached above  to  the  derma,  just  beneath  the  stratum  Mal- 
pighii,  and  below  to  the  hair  bulb.  When  it  contracts  it 
causes  the  hair  to  "stand  on  end" 

THE  NAILS. 

The  Nails  are  peculiar  appendages  that  serve  for  the 
protection  of  the  ends  of  the  fingers  and  toes,  and  consist  of 
the  ROOT  and  the  NAIL-BODY. 

The  ROOT  is  the  proximal  end  at  which  the  organ  grows. 
Here  the  epithelial  cells  are  transformed  into  the  hard  sub- 
stance that  gives  the  nail  its  character.  Along  the  sides, 
the  nail  is  protected  by  an  overhanging  ledge  of  skin,  which 
constitutes,  at  the  root,  the  NAIL-FOLD,  and  at  the  sides,  the 
NAIL-WALL.  The  angle  formed  by  the  nail  and  wall  is  the 


238 


THE    SKIN   AND   ITS   APPENDAGES. 


NAIL-GROOVE.  The  stratum  corneum  continues  into  the 
angle  over  the  edge  of  the  nail  as  the  EPONYCHIUM. 

The  NAIL-BODY  consists  of  the  NAIL  PROPER  and  the  NAIL- 
BED  upon  which  the  najl  rests. 

The  NAIL  represents  a  greatly  hypertrophied  stratum 
lucidum.  The  cells  are  flattened  elements,  in  which  the 
nuclei  are  indistinct,  and  the  protoplasm  clear.  At  the 
proximal  end  is  the  root,  and  at  this  place  alone  the  nail 
grows.  It  is  marked  by  a  white  area,  the  LUNULA.  Here 
the  epithelial  layer  is  so  thick  that  the  underlying  capil- 


FIG.  81. — CROSS- SECTION  OF  NAIL. 

i.  Nail;  2.  corium;  3.  epithelium;  4.  nail-wall;  5.  nail  groove;  6.  bone  of 
phalanx;  7.  eponychium. 

laries  are  invisible.      The  cells   also   are  said   to    contain 
keratohyalin  granules.     At  the  distal  end,  the  nail  projects 

as  the  FREE  EDGE. 

The  NAIL  BED  consists  of  the  stratum  Malpighii  and  the 
corium.  The  stratum  Malpighii  resembles  that  of  the  skin 
surface,  and  rests  upon  the  papillated  corium.  That 
portion  beneath  the  lunula  is  termed  the  MATRIX.  The 
corium  is  composed  of  bundles  of  white  fibrous  and  yellow 
elastic  tissues  that  have  a  general  longitudinal  direction. 
Between  the  bundles  are  vertical  fibres  that  pass  from  the 
periosteum  toward  the  nail.  The  PAPILLAE  of  the  bed  are 


GLANDS.  239 

not  like  those  of  the  skin,  but  consist  of  long  RIDGES  that 
extend  from  the  root  to  the  end  of  the  nail.  They  are 
small  beneath  the  root,  but  increase  *n  height  as  the  free 
edge  is  approached,  and  end  abruptly  at  that  point. 

THE  GLANDS. 

The  Glands  comprise  the  Sweat,  Sebaceous  and  Mam- 
mary Glands. 

The  Sweat-glands  are  of  the  coiled  tubular  variety. 
Each  consists  of  a  secretory  portion  that  lies  in  the  stratum 
reticulare,  and  an  excretory  duct  that  passes  up  through  the 
derma  and  cuticle  to  open  upon  the  surface. 

The  SECRETORY  PORTION  consists  of  a  single  layer  of  cu- 
boidal  cells  lining  the  tubule.  These  are  separated  from 
the  basement  membrane  by  a  layer  of  smooth  muscle  fibres. 
The  protoplasm  is  granular  and  may  contain  pigment 
granules  and  fat  globules.  The  nucleus  is  usually  quite 
distinct.  The  secretory  tubule  is  coiled  upon  itself,  and  the 
various  convolutions  are  separated  from  one  another  by 
interstitial  tissue  that  corresponds  to  the  tunica  propria. 

The  DUCT  that  leads  from  the  secretory  part  to  the  sur- 
face has  usually  one-half  the  diameter  of  the  secretory 
tubule,  and  is  lined  by  two  layers  of  cells  that  rest  upon  a 
basement  membrane  and  tunica  propria.  In  the  epidermis 
its  course  is  spiral,  and  no  separate  wall  is  present,  the  epi- 
thelial cells  of  the  epidermis  acting  in  this  capacity.  The 
diameter  of  this  portion  is  greater  than  that  of  the  corium. 
Its  opening  upon  the  surface  is  large  and  trumpet-shaped, 
and  is  called  the  SWEAT-PORE. 

These  glands  are  generally  distributed,  except  on  the 
margins  of  the  lips,  glans  penis  and  inner  surface  of  the 
prepuce.  They  are  most  numerous  in  the  palm  and 
largest  in  the  axilla.  The  average  diameter  is  i  mm.,  but 


240  THE    SKIN   AND   ITS   APPENDAGES. 

in  the  latter  region  they  may  attain  a  size  of  3  or  4  mm. 
In  this  region  the  secretory  tubule  may  be  branched. 

The  normal  secretion  is  an  oil  that  keeps  the  skin  soft  and 
pliable.  When  the  innervation  becomes  disturbed,  the 
secretion  becomes  thin  and  watery,  and  is  then  termed 
sweat.  The  GLANDS  of  MOLL,  of  the  eyelid,  and  the  CERU- 
MINOUS  GLANDS,  of  the  external  ear,  are  coiled  tubular 
glands  that  secrete  oil  alone. 

The  Sebaceous  Glands  are  racemose  structures.  They 
are  usually  found  in  connection  with  the  hair  follicles;  the 
largest  hairs  possess  small  glands,  while  the  smallest  hairs 
are  appendages  of  the  attached  sebaceous  glands.  Each 
is  surrounded  by  a  capsule  of  white  fibrous  tissue  that 
forms  the  supportive  structure. 

The  ALVEOLI  are  lined  by  cells  that  are  a  continuation  of 
the  cells  of  the  stratum  Malpighii,  and  which  rest  upon  a 
basement  membrane  and  tunica  propria.  These  cells  are 
very  large,  and  completely  fill  the  alveolus.  Those  in  the 
center,  where  the  lumen  should  be,  are  further  advanced  in 
changes  than  the  basal  cells.  The  entire  protoplasm  be- 
comes converted  into  oil,  which  constitutes  the  secretion, 
and  is  called  SEBUM.  The  death  of  the  cell  is  necessary  to 
the  formation  of  this  secretion.  The  transformed  cell  is 
immediately  replaced  by  another.  The  excretory  duct  is 
lined  by  several  layers  of  cells  that  do  not  take  part  in  the 
secretory  activity,  and  are  derived  from  the  outer  root 
sheath  of  the  hair  follicle. 

Sebaceous  glands  are  found  in  regions  devoid  of  hairs, 
as  in  the  margins  of  the  lips,  glans  penis,  prepuce,  glans 
clitoris  and  labia  minor  a. 

THE  MAMMARY  GLAND. 

The  Mammary  Gland  is  an  alveolo-tubular  organ.  Ac- 
cording to  some  writers,  it  is  a  modified  sweat  gland,  while 


MAMMARY    GLANDS. 


241 


others  hold  it  to  be  a  modified  sebaceous  structure.  It  is 
a  compound  organ,  if  such  a  term  may  be  used,  as  it  is 
composed  of  from  fifteen  to  twenty  individual  compound 
glands.  Each  of  these  possesses  its  own  excretory  duct, 
that  has  its  own  opening  in  the  nipple.  The  entire  organ 
is  covered  by  skin. 


•m 


FIG.    82. — SECTION    OF   LACTATING    HUMAN    MAMMARY    GLAND    (Stohr's 

Histology} . 
a.   Alveolo-tubule;    b.   tubule;   c.   duct;   d.   connective   tissue. 

Each  gland  consists  of  lobes  and  lobules  separated  and 
supported  by  white  fibrous  and  adipose  tissues.  All  of  the 
individual  glands  are  further  bound  together  in  the  same 
manner.  The  ducts  converge  and  end  in  the  nipple,  which 
forms  a  small  projecting  mass. 
16 


242  THE    SKIN   AND   ITS   APPENDAGES. 

Each  lobule  consists  of  a  number  of  acini,  which  are 
tubular  or  alveolar  in  structure.  The  number  of  these 
depends  upon  the  state  of  activity.  In  the  gland  of 
pregnancy,  the  acini  are  very  numerous,  and  are  lined  by 
simple  columnar,  or  cuboidal  cells,  in  which  are  accumulated 
the  fat  globules  that  form  the  important  constituent  of  the 
milk.  These  cells  rest  upon  a  basement  membrane,  but 
in  places  are  separated  therefrom  by  peculiar  elements 
called  basket  cells,  which  are  compared  to  the  smooth 
muscle  tissue  of  the  sweat  glands.  The  ducts  are  lined  by 
simple  columnar  cells  that  rest  upon  a  basement  membrane, 
outside  of  which  circular  bundles  of  white  fibrous  tissue 
are  to  be  found.  These  ducts  unite  to  form  the  main 
secretory  duct  of  the  individual  glands;  each  main  duct 
dilates  to  form  a  small  AMPULLA,  or  SINUS  LACTIFEROUS, 
before  the  nipple  is  reached. 

The  nonlactating  gland  consists  chiefly  of  white  fibrous 
and  adipose  tissues,  in  which  are  seen  a  number  of  ducts, 
but  few  acini.  The  bulk  of  the  organ  consists  of  the  fibrous 
and  adipose  tissues.  When  pregnancy  occurs,  the  ducts 
divide  and  redivide,  and  the  terminal  portions  dilate  to 
form  the  acini.  This  increase  in  the  glandular  part  causes 
the  increase  in  the  size  of  the  organ,  and  the  tingling 
sensation  that  occurs  at  that  time. 

After  lactation  has  ceased,  most  of  the  acini  undergo 
retrogression,  atrophy,  and  disappear.  Some  of  the  ducts 
undergo  the  same  change.  As  a  result,  the  gland  becomes 
somewhat  smaller  and  flabby.  In  old  age,  or  after  the 
child-bearing  period  has  passed,  the  glandular  and  ductular 
portions  retrograde  and  disappear  in  the  same  manner,  until 
in  old  age,  they  may  be  entirely  absent.  The  glands  are 
then  represented  by  fibrous  and  adipose  tissues. 

Milk  consists  of  minute  globules  of  fat,  o.i  to  0.5  mm. 
in  diameter,  surrounded  by  a  thin  layer  of  CASEIN.  This 


MILK.  243 

prevents  them  from  coalescing.  They  are  formed  in  the 
protoplasm  of  the  cells  of  the  acini,  but  the  cell,  after 
discharging  them,  does  not  die,  as  formerly  supposed.  At 
first,  COLOSTRUM  is  present  in  the  glands;  this  consists  of 
fat  and  COLOSTRUM  CORPUSCLES,  which  are  either  degen- 
erated gland  cells,  or  leukocytes. 

The  NIPPLE,  or  MAMMILLA,  consists  of  an  outer  covering 
of  pigmented  skin,  and  within  it  the  individual  ducts  are 
found.  These  are  separated  from  one  another  by  fibrous 
tissue  and  involuntary,  nonstriated  muscle.  The  muscle  tis- 
sue is  arranged  circularly  and  vertically,  extending  to  the 
apex  of  the  mammilla.  By  its  contraction,  an  erection  is 
produced.  Such  tissue  is  called  false  erectile  tissue.  At  the 
base  of  the  nipple  is  a  pigmented  area  called  the  AREOLA, 
which  contains  a  ring  of  sebaceous  glands  called  the  GLANDS 
OF  MONTGOMERY. 

In  addition  to  the  general  blood-vessels,  the  various  ap- 
pendages have  special  supplies.  From  the  sub  papillary  ar- 
terial plexus,  branches  pass  to  the  hair  follicles,  to  form  one 
plexus  beneath  the  hyalin  membrane,  and  another  in  the 
papilla.  The  venous  radicals  formed,  empty  into  subpapil- 
lary  plexus  of  veins.  Around  the  sebaceous  and  sweat 
glands,  the  subpapillary  arterial  plexus  forms  a  close  net- 
work of  capillaries  which  form  venous  branches  that  empty 
into  the  subpapillary  venous  plexus. 

The  blood-vessels  of  the  mammary  gland  converge  to- 
ward it,  and  pass  into  the  organ  in  the  partitions  between 
the  lobules.  From  these  vessels,  branches  extend  into  the 
lobules,  and  form  close  plexuses  around  the  acini. 

The  appendages  are  supplied  with  nerves  from  both  sym- 
pathetic and  cerebrospinal  systems.  The  hair  follicles 
receive  myelinated  fibres  that  branch  freely,  and  end  in 
spoon-shaped  masses  upon  the  glassy  membrane.  The 
sweat  glands  are  supplied  with  sympathetic  fibres,  that 


244  THE    SKIN    AND    ITS   APPENDAGES. 

form  a  close  network  beneath  the  basement  membrane, 
which  they  pierce,  to  end  upon  the  gland  cells.  The 
mammary  gland  has  both  varieties  of  nerves.  The  sym- 
pathetic are  the  more  numerous;  these  pass  to  the  blood- 
vessels on  the  one  hand,  and  to  the  acini  on  the  other.  In 
the  latter,  they  form  a  plexus  beneath  the  basement  mem- 
brane, and  from  this  plexus,  branches  end  upon  the  gland 
cells.  The  nerve  beginnings  in  the  nipple  are  numerous. 

The  glands  and  hair  follicles  are  surrounded  by  separate 
lymphatic  plexuses  that  empty  into  the  subcutaneous  ves- 
sels. In  the  mammary  gland,  plexuses  are  found  between 
the  individual  lobes,  around  the  ampullae  and  in  the  nipple. 
These  empty  into  the  axillary  lymphatics. 


CHAPTER  XVII. 


THE  NERVE  SYSTEM. 

The  Nerve  System  consists  of  the  Cerebrum,  Cerebellum, 
Pons,  Oblongata  and  Spinal  Cord.  It  is  surrounded  by  three 
membranes,  the  Dura,  Arachnoid  and  Pia. 

The  Dura  is  a  tough  membrane  composed  of  interlacing 
bundles  of  white  fibrous  and  yellow  elastic  tissues  that  con- 
tain lymph  spaces  between  them.  Within  the  skull,  it 
forms  the  inner  periosteum  of  the  cranium,  which  relation 
ceases  at  the  foramen  magnum,  the  entrance  into  the 
vertebral  canal.  In  the  latter,  it  is  not  connected  with  the 
bone,  but  hangs  like  a  bag  and  contains  the  spinal  cord. 
This  membrane  is  lined  by  endothelial  cells,  and  forms  the 
outer  boundary  of  the  SUBDURAL  LYMPH  SPACE.  It  is  quite 
vascular,  and  a  few  nerves,  that  pass  to  the  blood  spaces 
are  found. 

The  Arachnoid  is  a  thin,  delicate,  web-like  membrane 
composed  of  loosely  interwoven  bundles  of  wrhite  fibrous 
tissue.  It  lies  closely  applied  to  the  dura,  and  is  separated 
from  the  pia  by  the  SUBARACHNOIDEAN  LYMPH  SPACE. 
This  is  also  lined  by  endothelial  cells.  It  forms  the  PAC- 
CHIONIAN  BODIES  and  VILLI,  but  contains  neither  blood- 
vessels nor  nerves. 

The  Pia  is  the  vascular  membrane.  Its  outer  portion 
contains  the  bulk  of  the  vessels,  while  the  inner  enters  into 
close  relation  with  the  nerve  tissue.  Its  blood-vessels  lie 
in  the  fibro-elastic  network,  surrounded  by  PERIVASCULAR 
LYMPHATICS.  Its  arachnoidean  surface  is  covered  by 

245 


246  THE    NERVE    SYSTEM. 

endothelial  cells.  Only  a  few  nerve  fibres  are  present. 
The  pia  is  the  only  one  of  these  membranes  that  follows  the 
fissures  and  depressions  of  the  nerve  system. 

The  Nerve  System  consists  of  Gray  and  White  Substances. 

The  Gray  Substance  consists  of  NERVE  CELLS,  their 
PROCESSES  and  NEUROGLIA,  MYELINATED  and  AMYELINATED 
nerve  fibres. 

The  NERVE  CELLS  are  of  various  forms,  unipolar,  bipolar 
and  multipolar.  The  first  possess  but  one  process,  the 
second,  two,  and  the  third,  three  or  more.  The  CELL-BODY 
may  be  of  any  shape,  and  consists  of  granular  protoplasm 
that  has  a  fibrillar  structure.  The  NUCLEUS  is  usually 
large,  but  does  not  take  a  deep  stain.  The  NUCLEOLUS  is 
very  large  and  stains  deeply. 

The  PROCESSES  are  DENDRITIC  and  AXIS  CYLINDER.  The 
DENDRITES  are  minor  processes  that  are  subdivided  into  a 
great  many  smaller  processes,  the  teledendrites;  in  certain 
instances,  sensor  cells,  the  dendrites  may  be  myelinated 
(see  Nerve  Tissue,  p.  84).  The  AXIS  CYLINDER  process,  or 
NEURIT,  is  the  main  process.  In  cells  of  the  FIRST  TYPE,  or 
DEITER  CELLS,  the  neurit  leaves  the  gray  substance  to  become 
the  center  of  a  nerve  fibre.  In  those  of  the  SECOND  TYPE, 
or  GOLGI  CELLS,  the  axis-cylinder  never  leaves  the  gray 
substance. 

The  NEUROGLIA  consists  of  NEUROGLIA,  or  GLIA  CELLS,  and 
a  fibrillar  intercellular  substance.  The  cells  are  either 
spider  or  mossy.  For  a  detailed  description  of  these,  see  the 
chapter  on  Nerve  Tissues  (p.  86). 

The  White  Substance  consists  of  MYELINATED  NERVE 
FIBRES  held  together  by  NEUROGLIA  and  some  white 
fibrous  connective  tissue. 

In  the  Cerebrum  and  Cerebellum,  the  Gray  Substance  is 
external,  and  constitutes  the  CORTEX.  The  White  Sub- 
stance is  internal,  and  is  called  the  MEDULLA.  In  the 


THE    CEREBRUM.  247 

Spinal  Cord,  the  Gray  Substance  is  surrounded  by  the  White 
Substance.  In  the  Oblongata  and  Pons,  there  is  no  distinct 
arrangement. 

CEREBRUM. 

Beside  the  Cerebrum,  there  are  other  masses  of  nerve 
tissue  to  be  considered  here.  These  are  the  Olfactory 
Lobes,  the  Pituitary  and  Pineal  Bodies. 

The  GRAY  SUBSTANCE,  orCortexof  the  Cerebrum,  is  divided 
into  layers  that  are  not  sharply  limited  from  one  another. 
In  some  regions,  five  can  be  made  out,  in  others  three, 
while  four  form  the  average  number.  The  Cortex  is  made 
irregular  by  the  formation  of  tissues  and  convolutions. 
The  latter  consist  of  a  central  mass  of  white  substance, 
Medulla,  covered  by  the  gray  substance,  or  Cortex. 

The  CORTICAL  LAYERS  are,   from  without    inward,    the 

I,    MOLECULAR,   2,    SMALL   PYRAMIDAL,  3,    LARGE  PYRAMIDAL 

and  4,  MIXED  or  POLYMORPHOUS  LAYERS. 

1.  The  MOLECULAR  layer  consists  mainly  of  neuroglia  and 
cell-processes.     The  latter  are  derived  from   the  next  two 
layers,   and  are  chiefly  dendrites.     The  neuroglia  forms  a 
network  within  which  the  dendrites  and  myelinated  nerve 
fibres  lie.     The  latter  run  parallel  to  the  surface,  and  are 
therefore  called  tangential  fibres. 

Among  the  cellular  elements  are  some  of  the  second  type, 
or  Golgi  cells.  The  axis  cylinders  of  these  cells  remain  in 
the  gray  substance.  They  are  polygonal,  stellate  and 
spindle-shaped  cells,  in  which  the  dendrites  run  parallel  to 
the  surface,  and  are -called  the  CELLS  OF  CAJAL. 

2.  The     LAYER    OF    SMALL    PYRAMIDAL    Cells    is    Composed 

of  several  layers  of  cells,  the  dendrites  of  which  extend  into 
the  molecular  layer,  while  some  of  the  axis  cylinders  par- 
tially pass  to  the  molecular  layer  (second  type)  and  others 


248 


THE    NERVE    SYSTEM. 


pass  into  the  medulla  (first  type,  or  Deiter  cell)'.     In  the 
latter   case,    the    axis    cylinders    give   off    branches    called 


FIG.  83. — VERTICAL  SECTION  OF  HUMAN  CEREBRAL  CORTEX. 
a.  Pia;  b.  molecular  layer;  c.  small  pyramidal  cells;  d.  large  pyramidal  cells;  e. 
layer  of  polymorphous  cells;  /.  layer  of  fusiform  cells';  g.  medulla;  //. 
radial  bundles  of  myelinated  fibres  in  cortex;  i.  pial  process;  k.  large 
pyramidal  cell. 

collaterals.     The  CELLS  themselves  are  small,  measuring  10 
to  12  microns  in  diameter,  and  triangular  in  outline.     The 


THE    CEREBRUM.  249 

DENDRITES  arise  from  the  angles,  while  the  AXIS  CYLINDER, 
or  NEURIT,  has  its  origin  at  the  middle  of  the  base. 

3.  The  LAYER  OF  LARGE  PYRAMIDAL  cells  constitutes  the 
widest  and  most  important  layer.     The  CELLS  are  usually 
20  to  50  microns  in  diameter,  though  some  may  exceed  this. 
The  dendrites  pass  to  the  molecular  layer,  while  the  neurit 
becomes  myelinated  nerve  fibre.     These  cells  are,  therefore, 
cells  of  the  first  type.     Their  outline  is  triangular,  and  the 
nucleus  is  large  and  prominent. 

4.  The  LAYER  OF  POLYMORPHOUS  cells  contains  cells  of 
various  shapes;  these  are  large  and  small  pyramidal,  spindle- 
shaped,    oval    and    polygonal.     The    latter    predominate. 
The    dendrites    pass    to    the  upper  layers  of    the  cortex, 
while   the  axis  cylinders,  in  some  instances  remain  in  the 
cortex,  and  in  others  pass  into  the  medulla. 

In  the  last  three  layers,  bundles  of  myelinated  nerve 
fibres  having  a  radial  course  are  seen.  They  begin  in  the 
small  pyramidal  layer,  increase  in  number  as  they  ap- 
proach the  medulla,  and  contain,  beside  those  fibres  de- 
rived from  the  immediate  cortical  cells,  others  whose  origin 
is  not  definite. 

In  addition  there  are  other  myelinated  nerve  fibres  that 
form  layers  practically  parallel  with  the  surface.  The 
STRIATION  OF  BAiLLARGER  is  composed  of  such  fibres  that 
lie  in  the  large  pyramidal  cell  layer.  The  STRIATION  OF 
BECHTEREFF  consists  of  myelinated  fibres  between  molecu- 
lar and  small  pyramidal  cell  layers. 

The  Medulla  consists  of  MYELINATED  NERVE  FIBRES 
from  various  sources;  those  that  pass  to  the  periphery  of  the 
body  from  the  pyramidal  and  polymorphous  cells  (PRO- 
JECTION FIBRES)  ;  others  from  the  pyramidal  cells  that 
pass  from  one  hemisphere  to  the  other  (COMMISSURAL 
FIBRES)  ;  those  that  connect  different  areas  of  the  same 
side  (pyramidal  cells),  and  whose  axis  cylinders  are  UT" 


250  THE    NERVE    SYSTEM. 

branched,  and  pass  into  the  cortex  sooner  or  later  (AS- 
SOCIATION FIBRES);  lastly,  fibres  that  come  from  distant 
parts  of  the  same  or  the  other  hemisphere,  or  other  parts  of 
the  nerve  system  (CENTRIPETAL  FIBRES). 

OLFACTORY  LOBE. 

The  Olfactory  Lobe,  that  portion  of  the  nerve  system 
devoted  to  the  sense  of  smell,  is  comparatively  small  in 
man.  There  are.  five  layers  present,  which  are  best  marked 
in  the  central  part  of  the  organ.  These  are  the  LAYER  OF 

PERIPHERAL  FIBRES,  the  GLOMERULAR  LAYER,  the  MOLECU- 
LAR LAYER,  the  LAYER  OF  MITRAL  CELLS  and  the  GRANULE 
LAYER. 

The  LAYER  OF  PERIPHERAL  FIBRES  consists  of  a  plexus 
formed  by  the  fibres  of  the  OLFACTORY  NERVES. 

The  GLOMERULAR  LAYER  lies  beneath  the  above,  and  is 
made  up  of  peculiar  round,  or  oval,  bodies  100  to  300 
microns  in  diameter.  They  are  said  to  be  masses  of  inter- 
lacing telodendria  of  the  olfactory  and  mitral  cells. 

The  MOLECULAR  LAYER  is  made  up  of  large  and  small 
spindle-shaped  ganglion  cells  whose  dendrites  end  in  the 
glomeruli,  and  whose  axis  cylinders  pass  to  the  FIFTH,  or 

GRANULE  LAYER. 

The  LAYER  OF  MITRAL  CELLS  consist  mainly  of  large 
PYRAMIDAL  cells  varying  in  size  from  30  to  50  microns. 
Their  dendrites  pass  to  the  glomeruli  and  the  axis  cylinders 
to  the  granule  layer. 

The  GRANULE  LAYER  consists  of  nerve  cells  and  fibres. 
The  cells  are  stellate,  ganglion  elements,  and  peculiar  gran- 
ule cells;  the  latter  appear  to  have  no  axis  cylinders. 
Some  of  the  nerve  fibres  are  derived  from  the  mitral  cells, 
some  from  the  molecular  layer,  and  others  from  the  outside. 
The  deeper  bundles  enclose  granule  and  stellate  cells. 


THE    HYPOPHYSIS.  251 

THE  HYPOPHYSIS. 

The  Hypophysis  or  Pituitary  Body,  is  a  small  organ  con- 
sisting of  a  NEURAL,  or  CAUDAL  LOBE,  the  Posthypophysis 
and  an  EPITHELIAL,  or  FRONTAL  LOBE,  the  Prehypophysis. 
Both  are  surrounded  by  a  common  capsule  of  fibrous 
tissue. 

The  PREHYPOPHYSIS,  however,  is  divided  into  a  number 
of  tubular  alveoli  lined  by  polygonal  epithelial  cells.  These 
cells  are  of  two  varieties,  acidophilic  and  basophilic;  the 
latter  are  the  more  numerous.  Some  contain  large  nuclei 
surrounded  by  a  clear  and  slightly  granular  protoplasm, 
while  others  contain  a  similar  nucleus  buried  in  a  coarsely 
granular  protoplasm.  These  are  irregularly  arranged  so 
that  a  small  lumen  remains;  this  may  contain  colloid 
substance.  The  nerves  of  this  lobe  consist  of  very  few 
fibres  with  numerous  branchlets  and  ramifications  that 
follow  the  arteries  to  be  distributed  mainly  to  acini. 
Here  they  terminate  in  ball-like  enlargements. 

According  to  Berkley,  the  POSTHYPOPHYSIS  consists  of  an 
outer  layer  of  gray  substance  similar  to  that  of  the  infun- 
dibulum,  composed  of  slightly  irregular  endymal  cells  three 
to  four  layers  deep;  this  tissue,  however,  is  not  found  on  the 
surface  where  the  two  lobes  are  in  contact.  The  central 
part  of  this  lobe  consists  of  a  few  acini,  that  may  contain 
colloid  substance;  these  acini  constitute  about  one-third  of 
the  cellular  elements;  the  remaining  two-thirds  of  the  cellu- 
lar elements  are  nerve  cells  of  various  forms  as  follows:  i. 
Flask-shaped  cells  with  short  axones  and  knob- tipped  den- 
drites.  These  cells  are  widely  distributed  and  the  branches 
end  freely  between  the  other  structures.  2.  Cells  whose 
processes  end  in  the  endymal  layer;  these  are  large  ganglion 
cells  the  axones  of  which  traverse  the  entire  organ  and  end 
in  the  infundibular  area.  Large  oval  cells  higher  up  also 


252  THE   NERVE    SYSTEM. 

belong  to  this  group.  3.  Small  elements  with  short  den- 
drites  of  a  prickly  appearance;  these  cells  are  unlike  any 
other  cells  in  the  body.  To  this  group  belongs  another 
small  cell  with  an  apical  tuft  of  wavy  processes. 

The  two  lobes,  although  surrounded  by  an  apparently 
common  capsule,  are  absolutely  distinct  and  are  separated  by 
a  fibrous  lamella.  The  posthypophysis  alone  is  connected 
with  the  infundibulum. 

The  arteries  reach  the  organ  by  means  of  the  infun- 
dibulum. As  they  reach  the  fibrous  septum  between  the 
two  lobes  branches  pass  to  the  prehypophysis  and  form 
plexuses  between  the  acini.  The  capillary  plexuses  of  the 
posthypophysis  are  likewise  numerous.  The  veins  have  a 
corresponding  return  course. 

The  lymphatics  are  found  in  the  lamella  between  the 
two  lobes  and  consist  of  a  network  of  spaces  lined  by 
simple  ciliated  cells;  these  probably  represent  endymal 
cells  derived  from  the  cavity  of  the  infundibulum. 

THE  EPIPHYSIS. 

The  Epiphysis,  or  Pineal  Body,  is  a  small,  apparently 
unimportant  organ  in  man.  In  some  lower  animals,  it  is  a 
visual  organ.  This  rudimentary  structure  consists  of  a 
number  of  tubules  lined  by  polygonal  cells  supported  by 
fibrous  tissue  and  neuroglia  in  the  lower  part.  These 
tubules  contain  the  BRAIN  SAND,  or  ACERVULUS  CEREBRI, 
peculiar  concretions  of  phosphate  and  carbonate  of  mag- 
nesium, ammonium  and  calcium,  which  are  not  limited  to 
this  body,  however,  but  may  be  found  in  other  portions  of 
the  nerve  system. 

CEREBELLUM. 

The  Cerebellum,  or  Little  Brain,  has  a  characteristic 
gross  appearance,  when  sectioned.  Its  Cortex  and  Medulla 


THE    CEREBELLUM. 


253 


are  so  colored  and  arranged  as  to  give  the  appearance  of 
a  TREE,  called  the  ARBOR  VITAE,  or  TREE  OF  LIFE. 


FIG.  84. — VERTICAL  SECTION  OF  THE  HUMAN  CEREBELLUM. 
A.  Cerebellum,  low  power;  B.  cerebellum  highly  magnified;  a.  molecular  and 
ganglionic   1  yers;    b.  granule   layer;   c.  medulla;   d.  pia;  e.  cell  of  Pur- 
kinje;  /.  cell  of  molecular  layer;  g.  cells  of  the  granule  layer;  C.  cell 
of  Purkinje. 

The  Cortex  consists  of  three  sharply-marked  layers,  the 

I,   MOLECULAR, rthe  2,  GANGLIONIC  and  3,  GRANULE  LAYERS, 

from  without  inward. 


254  THE   NERVE    SYSTEM. 

1.  The  MOLECULAR  LAYER  consists  of  a  network  of  neuro- 
glia,  in  which  the  dendritic  branches  of  the  cells  of  the  lower 
layers  are  found.     They  are  mostly  those  of  the  GANGLIONIC 
CELLS.     In  addition,  there  are  small  and  large  multipolar 
cells;  the  axis  cylinders  of  the  former  remain  in  this  layer, 
while  those  of  the  latter  pass  toward  the  second  layer  and 
form  a  network,  of  branches  around  the  ganglionic  cells. 
They  are  therefore  called  the  BASKET  CELLS.     Fibres  from 
the  MEDULLA  pass  into  this  layer  and  break  into  a  great 
number  of  delicate  terminal  twigs. 

2 .  The  GANGLIONIC  LAYER,  Or  LAYER  OF  PURKIN  JE  CELLS,  is 

very  characteristic.  The  bodies  of  these  cells  are  very  big, 
measuring  30  to  70  microns.  A  large  nucleus  and  a  dis- 
tinct nucleolus  are  present.  The  protoplasm  is  fibrillar, 
but  contains  no  pigment  granules.  Two  main  processes 
extend  from  the  body;  the  LOWER,  or  NEURIT,  passes  to  the 
medulla  and  becomes  a  myelinated  nerve  fibre.  The 
UPPER,  or  DENDRITIC,  quickly  breaks  into  two,  that  run  at 
right  angles  to  the  main  stem.  From  the  upper  sides  of 
these  two  branches,  an  immense  number  of  small,  delicate 
branches  are  formed.  These  cells  are  called  ANTLER  CELLS, 
from  their  appearance.  The  cells  are  more  numerous  at 
the  top  than  at  the  bottom  of  the  convolutions. 

3.  The  GRANULE  LAYER  IS  Composed  of  GREAT  and  SMALL 

GRANULE  CELLS.  The  SMALL  CELLS  possess  large  nuclei  and 
a  small  amount  of  protoplasm.  The  DENDRITIC  PROCESSES 
remain  mostly  in  this  layer,  while  the  NEURIT  passes  to  the 
molecular  layer,  forming  UT"  branches  that  run  parallel  to 
the  surface.  The  LARGER  CELLS  resemble  the  cells  of  the 
ganglionic  layer,  but  the  AXIS-CYLINDER  forms  a  network  of 
branches,  being  a .  cell  of  the  second  type.  Besides  the 
neuroglia  present,  there  are  some  fibres  of  the  myelinated 
variety.  This  layer  is  thicker  at  the  summit  of  the  convolu- 
tion, and  diminishes  as  the  base  is  reached. 


THE    PONS.  255 

The  Medulla  consists  of  myelinated  nerve  fibres,  sup- 
ported by  neuroglia  and  connective  tissue;  of  these  fibres, 
some  form  the  inferior  peduncles;  others  the  middle  (pontile), 
and  the  remainder  the  superior  peduncles,  which  connect 
the  cerebellum  with  the  corpora  quadrigemina. 

THE  PONS. 

The  Pons  can  conveniently  be  divided  into  two  portions, 
the  VENTRAL  PART  or  PONS  PROPER,  that  can  readily  be 
distinguished  by  the  naked  eye,  and  the  DORSAL  or  TEG- 
MENTAL  PART,  which  is  continuous  with  the  oblongata,  and 
hence  called  PREOBLONGATA. 

The  ventral  portion  consists  mainly  of  FIBRES  running  in 
various  directions  and  separated  by  masses  of  gray  sub- 
stance, the  PONTILE  NUCLEI.  The  FIBRES  course  trans- 
versely and  longitudinally. 

The  transverse  fibres,  at  the  caudal  portion  of  the  pons  lie 
superficial  to  the  pyramids;  at  a  higher  level  the  fibres  hv 
crease  in  number  and  are  often  described  in  three  groups: 
a.  Ventral  superficial  fibres,  those  that  pass  ventral  to  the 
pyramids;  b.  dorsal,  or  deep,  fibres,. those  that  pass  dorsal 
to  the  pyramid;  c.  penetrating,  or  middle,  those  that  pass 
right  through  the  pyramids  and  break  into  a  number  of 
smaller  bundles.  At  the  cephalic  level  of  the  pons  all  the 
transverse  fibres  again  form  a  single  mass.  At  the  lateral 
border  of  the  pons  these  transverse  fibres  pass  into  the 
cerebellum  as  the  medipeduncles.  As  to  origin  these  fibres 
are  of  two  kinds :  i .  those  that  arise  in  the  cerebellar  cortex 
and  end  in  the  pon tile  nuclei  and,  2.  those  that  arise  in  the 
pontile  nuclei  and  end  in  the  cerebellar  cortex. 

The   longitudinal   fibres   are    those    that    constitute    the 

pyramid ;  at  the  upper  and  lower  portions  of  the  pons  these 

•  fibres  form  a  single  compact  bundle,  while  in  the  middle 


256 


THE   NERVE    SYSTEM. 


region    they   are   separated   into   smaller   bundles   by    the 
transverse  penetrating  fibres. 

The  gray  substance  of  this  portion  of  the  pons  consists  of 


FIG.  85.— DIAGRAM  OF  TRANSVERSE  SECTION  OF  CEPHALAD 

PORTION  OF  PONS  (Morris,  after  Schwalbe}. 

i,  Mesencephalic  root  of  trigeminal  nerve;  2,  prepeduncle;  3,  Median  longi- 
tudinal bundle;  4,  lateral  lemniscus;  5,  formatio  reticularis;  6,  medial 
lemniscus;  7,  trigeminal  nerve;  8,  pyramidal  fasciculi;  9,  transverse  fibers 
of  pons;  10,  raphe;  n,  fourth  ventricle;  12,  metatela. 

many  collections  of  nerve  cells  in  -the  spaces  between  the 
fibre  bundles;  these  are  the  pontile  nuclei. 

At  the  boundary  zone  between  pons  and  preoblongata 
lies  a  bundle  of  transverse  fibres  that  arise  from  cells  in  the 
nuclei  of  termination  of  the  cochlear  division  of  the  auditory 
nerve;  these  fibres  cross  to  the  opposite  side  of  the  organ 


THE    PONS. 


257 


and  form  here  in  the  mesial  region,  by  their  decussation, 
the  trapezium.  From  the  trapezium  the  fibres  continue 
toward  the  side  of  the  preoblongata  and  form  here  the 
lateral  lemniscus,  which  will  be  described  later. 

The  PREOBLONGATA,  or  TEGMENTAL  PORTION  of  the    pons, 

lies  dorsal    to  the  preceding    structures  and  includes  the 


FIG.  86 — DIAGRAM  OF  TRANSVERSE  SECTION  OF  CAUDAL  PORTION 

OF  PONS  (Morris,  after  Schwalbe) . 

i,  Nucleus  of  abducens  (6th)  nerve;  2,  lateral  nucleus  of  vestibular 
nerve;  3,  formatio  reticularis;  4,  nucleus  of  facial  (yth)  nerve;  5,  spinal 
tract  of  trigeminal  (5th)  nerve;  6,  root  of  vestibular  nerve;  7,  superior 
olive;  8,  root  of  abducens  (6th)  nerve;  9,  pyramid;  10,  trapezium;  n, 
raphe;  12,  descending  root  of  facial  (yth)  nerve;  13,  genu  of  facial 


cephalic  portion  of  the  floor  of  the  fourth  ventricle.  The 
gray  substance  is  found  mainly  as  a  layer  just  beneath  the 
endyma  of  the  ventricle;  at  various  levels  it  forms  nuclei 
of  origin  (motor)  or  termination  (sensor)  of  the  trigeminal, 
abducens,  facial  and  auditory  nerves.  Between  these 
nuclei  and  the  trapezium  is  found  the  FORMATIO  RETICU- 
17 


258  THE    NERVE    SYSTEM. 

LARIS.  Beneath  the  ventricle  gray  and  near  the  midline  is 
a  bundle  of  fibres,  the  MEDIAN  LONGITUDINAL  BUNDLE. 
Laterally  is  formed  a  bundle  of  ascending  fibres  constituting 
the  continuation  of  the  fibres  of  the  trapezium,  called  the 

LATERAL    LEMNISCUS. 

The  MEDIAL  LEMNISCUS  continued  cephalad  from  the 
oblongata  is  seen  near  the  midline  in  the  lower  part  of 
preoblongata,  but  higher  up  it  is  pushed  laterad  by  other 
structures,  so  that  it  lies  here  in  relation  with  the  lateral 
lemniscus,  but  is  not  connected  therewith. 

The   PREPEDUNCLE,  Or   SUPERIOR  CEREBELLAR  PEDUNCLE, 

is  found  only  in  the  middle  and  upper  portions  of  the 
preoblongata,  occupying  a  superficial  position  in  the  dorso- 
lateral  area;  higher  up  it  becomes  covered  by  the  lateral 
lemniscus. 

In  addition  to  the  cranial  nerve-nuclei  several  other 
gray  masses  of  importance  are  seen  in  the  preoblongata. 
The  NUCLEUS  OF  THE  LATERAL  LEMINSCUS  is  seen  at  the  side 
of  the  organ  and  represents  a  nucleus  of  termination  of  some 
of  the  fibres  of  the  trapezium;  its  cells  give  rise  to  fibres 
that  continue  cephalad  in  the  lateral  lemniscus.  This 
nucleus  seems  to  be  connected  with  the  succeeding  nucleus. 

The  SUPERIOR  OLIVARY  NUCLEUS  lies  just  laterad  of  the 
trapezium  and  many  of  the  fibres  of  the  trapezium  end  here; 
its  cells  give  rise  to  fibres  that  aid  in  the  formation  of  the 
lateral  lemniscus.  This  nucleus  lies  at  a  lower  level 
(caudad)  than  the  preceding,  but  seems  connected  with  it. 

THE  OBLONGATA. 

The  Oblongata,  or  Postoblongata,  consists  of  halves  like 
the  spinal  cord,  but  here  the  resemblance  ceases,  as  the  ar- 
rangement of  gray  and  white  substances  is  different.  The 
H-shape  of  the  gray  substance  is  no  longer  retained;  that 


THE    OBLONGATA.  259 

portion  in  relation  with  the  canal  still  remains  about  the 
same,  but  the  horns  are  modified  and  broken  by  the 

PYRAMIDAL   DECUSSATION    and    the    FORMATIO    RETICULARIS. 

As  the  canal  is  followed  upward  and  is  seen  to  broaden  into 
the  fourth  ventricle,  or  METEPICELE,  the  gray  substance 
that  surrounded  the  canal  becomes  merely  the  floor  of  the 
ventricle.  The  remaining  gray  is  seen  as  isolated  masses 
forming  nuclei,  as  the  GRACILE,  CUNEATE,  OLIVARY,  ARCUATE 

and  PYRAMIDAL  NUCLEI. 

The  SUBSTANTIA  GELATINOSA  ROLANDI  continues  from 
the  spinal  cord  as  the  same  mass  forming  a  cellular  mass 
at  the  side  of  the  oblongata,  the  TUBERCULUM  ROLANDI. 

The  cause  of  the  rearrangement  of  the  ventral  gray  sub- 
stance is  the  PYRAMIDAL  DECUSSATION.  As  the  motor 
fibres  that  compose  the  pyramid  are  about  to  enter  the  cord, 
85  to  90  per  cent,  take  an  oblique  course  from  the  ventral 
to  the  lateral  portion  of  the  opposite  side  of  spinal  cord,  con- 
tinuing here  as  the  crossed  pyramidal  tract.  In  crossing, 
the  ventral  horn  of  gray  substance  is  cut  into  two  portions, 
that  around  the  canal  the  basal  part  and  the  isolated 
ventral  mass  that  is  pushed  laterad.  The  ventral  ground 
bundle  of  the  oblongata  becomes  covered  by  the  pyramid  so 
that  the  bundle  becomes  more  dorsally  placed  as  the 
oblongata  is  ascended. 

In  the  caudal  portion  of  the  oblongata  other  marked 
changes  are  noted  dorsally.  As  the  funiculus  gracilis  (Goll) 
and  the  funiculus  cuneatus  (Burdach)  enter  the  oblongata 
from  the  spinal  cord  they  form  two  broad  masses  that  con- 
sequently force  the  dorsal  gray  horns  laterad  so  that 
ultimately  these  gray  masses  lie  opposite  each  other  at  the 
sides  of  the  oblongata.  Ultimately  the  basal  (canal)  and 
lateral  portions  of  the  gray  substance  become  separated 
from  each  other  by  nerve  fibers  that  run  in  various  direc- 
tions, constituting  the  FORMATIO  RETICULARIS.  Thus,  as 


260  THE    NERVE    SYSTKM. 

ventrally,  the  gray  substance  of  the  dorsal  horn  becomes 
separated  into  a  basal  (canal)  portion  (connected  with  the 
ventral  basal  gray)  and  an  isolated  lateral  mass,  that  is 
associated  with  the  spinal  root  of  the  trigeminal  nerve. 


FIG.  87. — SECTION  OF  THE  OBLONGATA  AT  ABOUT  THE  MIDDI.K  OF 

THE  OLIVARY  BODY   (Gordinier,  ajter  Schwalbe}. 

j.l.a.,  Ventro-median  fissure;  n.ar,  arcuate  nucleus;  p,  pyramid;  A"II, 
hypoglossal  nerve;  j.a.e.,  external  arcuate  fibers:  n  ./.,  nucleus  lateralis;  g, 
substantia  gelatinosa;  a.V.,  ascending  root  of  fifth  nerve;  X,  vagus  nerve; 
/.r.,  formatio  reticularis;O.,  restis  being  formed;  n.c.,  nucleus  cunealus; 
f.s.,  funiculus  solitarius;  n.X,  and  n.X',  two  portions  of  vagal  nucleus; 
nXIT,  hypoglossal  nucleus;  r,  raphe;  A,  beginnings  of  ventral  column  of 
the  spinal  cord;  of  o",  accessory  olivary  nuclei;  p.o.L,  peduncle  of  olive; 
n.am,  nucleus  ambiguus. 

In  connection  with  this  dorsal  basal  gray  arise  two  new  gray 
masses,  the  NUCLEUS  GRACILIS  and  NUCLEUS  CUNEATUS. 

The  NUCLEUS  GRACILIS  is  a  mass  of  gray  substance  that 
lies  close  to  the  dorso-median  groove  and  increases  in  size  as 
the  funiculus  gracilis  ends.  It  represents  the  nucleus  of 


THE    OBLONGATA. 


261 


termination  of  the  fibres  of  the  funiculus  gracilis,  or  column 
of  Goll.  The  cephalic  end  of  this  nucleus  is  connected  with 
the  gray  substance  of  the  canal  area. 

The  NUCLEUS  cuNEATUvS  lies  laterad  of    the  preceding; 


FIG.  88. — TRANSVERSE  SECTION  OF  THE  OBLONGATA  THROUGH  THE 

MOTOR  DECUSSATION.   (Goedinier,  after  Henle) . 

Fpy,  Ventral  pyramid;  Cga,  ventral  horn;  Fa,  beginning  of  ventral  column 
of  spinal  cord;  Ng,  nucleus  gracilis;  g,  substantia  gelatinosa;  XI,  spinal 
accessory  nerve. 

at  its  origin  it  is  connected  with,  and  represents  an  offshoot 
of,  the  central  gray  substance.  It  is  the  nucleus  of  termina- 
tion of  the  fibres  of  the  funiculus  cuneatus. 

Cephalad    to    the   motor,   or   pyramidal   decussation,  is  a 
second  crossing  of  fibres  involving  those  of  sensor  function, 


262  THE    NERVE    SYSTEM. 

tllC    SICNSOK    I)ECrSSATH)\,    or    DECUSSATION    OF    1IIK    FILLET, 

After  crossing  the  midline  the  fibres  form  a  bundle  called 
the  FILLET,  or  MEDIAL  LEMNiSCUS.  These  ascending  fibres 
arise  in  the  nuclei  gracilis  cuneatus,  and  in  crossing  have  also 
been  termed  the  DEEP,  or  INTERNAL  ARCUATE  FIBRES. 

The  INFERIOR  OLIVARY  NUCLEUS,  or  BODY,  is  an  isolated 
mass  of  gray  and  white  substances  located  in  the  ventro- 
lateral  region  of  the  oblongata.  The  gray  substance  is 
peripherally  placed  in  the  form  of  a  thick  wavy  lamina  that 
is  wanting  at  the  mesial  side  of  the  body;  this  space  is  the 
hilum.  The  central  part  of  the  body  consists  of  myelinated 
nerve  fibres  that  leave  or  enter  through  the  hilum.  In  the 
immediate  neighborhood  of  the  olive  are  two  smaller  gray 
masses,  the  dorsal  and  mesial  accessory  olivary  nuclei. 

The  ARCUATE  NUCLEUS  is  found  along  the  ventral  portion 
of  the  oblongata  cephalad  to  the  pyramidal  decussation. 
It  is  a  flattened  mass  of  gray  substance;  here  end  some 
of  the  fibres  of  the  superficial  arcuate  band,  while  other 
fibres  of  this  band  arise  from  the  cells  of  this  nucleus. 

The  FORMATIO  RETICULARIS  lies  in  the  lateral  area  of  the 
oblongata  and  consists  of  a  network  of  gray  and  white  sub- 
stances. The  gray  is  more  abundant  laterally  and  this 
portion  thence  receives  the  name  formatio  reticularis 
grisea.  The  cells  are  associative  in  function  and  serve  to 
connect  the  various  levels  of  the  oblongata  with  one  another. 
The  formatio  near  the  midline  is  almost  devoid  of  nerve 
cells  and  is  called  the  formatio  reticularis  alba.  The  fibers 
of  the  formatio  have  both  a  transverse  course  (deep  ^arcuate 
fibres]  and  a  longitudinal  direction. 

The  RESTIS,  RESTIFORM  BODY,  or  inferior  CEREBELLAR 
PEDUNCLE,  is  found  in  the  dorsal  portion  of  the  oblongata. 
It  is  composed  of  the  direct  cerebellar  fibres  of  the  spinal 
cord;  fibres  from  the  nuclei  gracilis  and  cuneatus  of  the  same 
side,  the  dorsal  superficial  arcuate  fibres;  fibres  from  the  oppo- 


THE    SPINAL    CORD.  263 

site  nuclei  gracilis  and  cuneatus,  the  -ventral  superficial  arcuate 
fibres;  fibres  from  the  opposite  olivary  body,  the  olivo-cere- 
bellar  fibres.  The  last  seem  to  form  the  bulk  of  the  restis. 

The  LATERAL  TRACT  consists  of  fibres  of  the  lateral 
ground  bundle  of  the  spinal  cord  and  fibres  of  the  lateral 
columns,  not  including  the  direct  cerebellar  and  crossed 
pyramidal  tracts.  The  ground  bundle  fibres  enter  into  the 
formation  of  the  formatio  reticularis,  while  the  remaining 
fibres  continue  toward  the  cerebrum. 

The  VENTRAL  PYRAMID,  or  pYRAMis,  consists  of  motor 
fibres  from  higher  centers  to  the  spinal  cord. 

THE  SPINAL  CORD. 

This  portion  of  the  nerve  system  is  the  longest.  It  is 
characterized  by  possessing  the  gray  substance  internally 
and  the  white  substance  externally.  Its  form  varies  in  the 
different  regions;  in  the  cervical  and  lumbar  areas,  it  is 
enlarged,  and  these  enlargements  are  termed  the  IN- 
TUMESCENITA  CERVICALIS  and  LUMBALis,  respectively. 
The  outline  in  the  cervical  region  is  oval,  in  the  thoracic 
region  almost  circular,  and  in  the  lumbar  portion  oval. 

The  cord  ends  in  the  neighborhood  of  the  upper  border 
of  the  second  lumbar  vertebra,  and  its  termination  is  cone- 
shaped.  This  is  called  the  CONUS  MEDULLARIS.  Owing  to 
the  fact  that  the  cord  is  shorter  than  the  vertebral  canal, 
the  lower  lumbar,  the  sacral  and  coccygeal  nerves  pass  down 
for  varying  distances  before  reaching  their  respective  fora- 
mina. This  produces  a  mass  of  fibres  in  the  lower  part  of 
the  canal  called  the  CAUDA  EQUINA.  In  the  center  of  the 
latter  is  a  fibrous  band  that  extends  toward  the  end  of  the 
canal.  It  is  the  FILUM  TERMINALE. 

The  Cord  consists  of  two  hemispheres  separated  ventrally 
by  the  VENTRAL,  or  ANTERIOR  MEDIAN  FISSURE,  in  which  is 


264 


THE   NERVE    SYSTEM. 


seen  a  process  of  the  pia.     Dorsally,  no  fissure  exists,  but  a 
SEPTUM    is   present.     This    is    the    DORSAL,    or    POSTERIOR 

MEDIUM  SEPTUM,  Or  RAPHE. 

The  gray  substance  of  the  cord  is  arranged  in  the  form  of 
a  letter  H,  the  two  side  bars  constituting  the  HORNS,  and 


FIG.  89 — A  COMPOSITE  DIAGRAM  OF  ALL  LEVELS  OF  THE  SPINAL  CORD. 

i,  Sulco-marginal  tract;  2,  direct  pyramidal  tract  (Tiirck);  3,  ventral  ground 
bundle;  4,  vestibulo-spinal  tract  (Loewenthal);  5,  ventro-median  group 
of  cells;  6,  central  group  of  cells;  7,  spino-olivary  tract  (Helweg);  8,  ven- 
tro-lateral  group  of  cells;  9,  tract  of  Gowers;  10,  lateral  ground  bundle; 
n,  dorso-median  group  of  cells;  12,  mixed  lateral  tract;  13,  spino-thal- 
amic  tract;  14,  rubro-spinal  tract;  15,  dorsal  nucleus  (Clarke);  i63 
crossed  pyramidal  tract;  17,  cell  group  of  dorsal  horn;  18,  direct  cere- 
bellar  tract;  19,  dorsal  (sensor)  root;  20,  tract  of  Spitzka  (marginal); 
21,  dorsal  ground  bundle;  22,  dorso-external  column  (Burdach);  23,  cornu- 
commissural  tract;  24,  dorso-internal  column  (Goll);  25,  comma  tract  of 
Schutze;  26,  septomarginal  tract  (Bruce);  27,  oval  bundle  of  Flechsig. 

the  cross-bar  the  GRAY,  DORSAL,  or  POSTERIOR  COMMISSURE. 
The  HORNS  are  further  subdivided  into  VENTRAL,  or 
ANTERIOR,  and  DORSAL,  or  POSTERIOR.  In  the  thoracic 
region  a  LATERAL  HORN  is  described. 


THE    SPINAL    CORD.  265 

The  VENTRAL  HORNS  are  large  and  blunt,  and  do  not  ex- 
tend to  the  periphery.  In  them  are  found  collections  of 
large,  multipolar  ganglion  cells  having  a  MOTOR  function. 
The  axis  cylinders  of  the  cells  pass  out  of  the  ventral  portion 
of  the  cord  as  the  VENTRAL  ROOT  OF  THE  SPINAL  NERVE. 
These  cells  average  60  to  120  microns,  and  are  quite 
numerous.  Each  is  surrounded  by  a  distinct  lymph  space. 
They  are  collected  into  various  groups  which  vary  according 
to  the  region  of  the  cord.  The  following  are  the  most 
important:  i.  CERVICAL  REGION:  VENTRO-MEDIAN,  DORSO- 
MEDIAN,  VENTRO-LATERAL,  INTERMEDIATE,  DORSO-LATERAL. 
2.  THORACIC  REGION:  VENTRAL,  INTERMEDIATE.  3.  LUM- 
BAR REGION:  VENTRO-MEDIAN,  CENTRAL,  VENTRO-LATERAL, 

DORSO-LATERAL   (see  Fig.   89). 

The  DORSAL,  or  POSTERIOR  HORNS  are  sharp  and  pointed, 
and  usually  extend  to  the  edge  of  the  cord.  The  cells  here 
are  small  in  number  and  size,  averaging  from  15  to  20  mi- 
crons, and  are  scattered  along  the  external  margin.  They 
comprise  'marginal  cells  whose  axis  cylinders  pass  into  the 
lateral  columns  after  passing  through  the  substantia  gelatin- 
osa;  spindle-shaped  cells,  the  neurits  of  which  pass  into  the 
dorsal  columns;  stellate  cells,  the  axis  cylinders  of  which 
pass  into  the  dorsal  columns  of  Burdach. 

The  LATERAL  HORNS  are  most  marked  in  the  thoracic  and 
upper  cervical  and  third  and  fourth  sacral  regions.  Each 
is  formed,  chiefly,  by  the  intermediate  cell  group.  The 
axones  of  these  cells  probably  do  not  pass  into  the  ventral 
roots  but  terminate  within  the  cord  at  various  levels  of 
the  same  and  opposite  sides.  They  are  probably  closely 
connected  with  the  sympathetic  system  and  vasomotor  and 
sweat-gland  nerves. 

Along  the  median  edge  of  the  horn,  near  its  junction  with 
the  gray  commissure,  lies  a  group  of  cells  that  extends  from 
the  cervical  to  the  mid-lumbar  region.  This  is  the  VESICU- 


266 


THE    NERVE    SYSTEM. 


II  10 


13   12 


FIG.  90.— CROSS-SECTION  OF  HUMAN  SPINAL  CORD  AT  LOWER  CERVICAL 
REGION.     From  Decapitated  Criminal  (Dr.  H.  H.  Gushing). 

i.  Ventral  spinal  artery;  2.  pial  process  in  ventral  fissure;  3.  dura;  4.  nerve 
fibres  from  ventral  horn  (motor  root  fibres);  5.  stellate  cells  of  ventral 
horn;  6.  ventral  horn;  7.  dorsal  horn;  8.  nerve  fibres  of  dorsal  horn 
(sensor  root  fibres);  9.  dorsal  septum;  10.  dorsal  spinal  artery  and  vein 
(arteria  et  vena  fissurae  posterioris) ;  n.  fibres  of  the  column  of  Goll; 
12.  tissue  separating  the  columns  of  Goll  and  Burdach;  13.  column  of 
Burdach;  14.  traces  of  the  lateral  horn;  15.  fibres  of  the  lateral  columns; 
17.  central  canal  in  the  gray  commissure;  18.  ventral,  or  white  com- 
missure; 19.  fibres  of  the  ventral  columns;  20.  arteria  et  vena  fissurae 
anterioris. 


THE    SPINAL    CORD.  267 

LAK  COLUMN  OF  CLARK.  A  similar  collection,  though  less 
distinct,  lies  just  ventral  of  Clark's  column  and  extends 
through  a  greater  part  of  the  cord.  This  is  the  NUCLEUS  OF 
STILLING  and  is  represented  in  the  oblongata  by  the 
accessory  cuneate  nucleus. 

The  neurits  of  these  cells  of  the  DORSAL  HORNS  pass  into 
the  DORSAL  COLUMNS;  those  of  the  VESICULAR  COLUMN  OF 
CLARK  pass  into  the  DIRECT  CEREBELLAR  TRACT,  on  the 
same  side  and  into  the  VENTRAL  (ANTERIOR)  COMMISSURE. 
In  the  dorsal  horn  is  the  SUBSTANTIA  GELATINOSA  ROLANDI, 
which  consists  of  cells  of  the  second  type  (Golgi). 

The  GRAY  COMMISSURE  consists  of  myelinated  and 
amyelinated  commissural  fibres  separated  into  VENTRAL 
(smaller)  and  DORSAL  (larger)  bands  by  the  CENTRAL 
CANAL  of  the  cord.  The  ventral  portion  is  called  the 
VENTRAL,  or  ANTERIOR  GRAY  COMMISSURE,  while  the  other 
receives  the  name  of  DORSAL,  or  POSTERIOR  GRAY  COM- 
MISSURE. The  whole  is  the  GRAY,  or  DORSAL  COMMISSURE, 
in  contradistinction  to  the  VENTRAL,  or  WHITE  COMMISSURE. 

The  CANAL  of  the  cord  is  the  remains  of  the  embryonal 
cavity  within  this  portion  of  the  nerve  system.  In  child- 
hood, it  is  lined  by  simple  ciliated  elements,  the  ENDYMAL 
CELLS.  Above,  it  communicates  with  the  fourth  ventricle, 
and  its  form  varies  in  the  different  portions  of  the  cord.  It 
becomes  more  or  less  obliterated  with  increasing  age,  par- 
tially by  increased  growth  of  the  lining  ENDYMAL  cells  and 
partially  by  the  ingrowth  of  neuroglial  processes. 

Besides  the  nerve  cells,  processes  and  fibres,  the  gray 
matter  contains  that  peculiar  supportive  tissue  found  only 
in  the  nerve  system,  called  NEUROGLIA.  This  substance 
is  ectodermal  in  origin. 

NEUROGLIA  consists  of  two  varieties  of  cells,  or  astrocytes, 
SPIDER  and  MOSSY.  The  SPIDER  cells  are  composed  of  thin, 
flat  bodies  from  which  extend  long,  slender  processes.  The 


268  THi:    NERVE    SYSTEM. 

MOSSY  cells  have  short,  heavy  processes.  In  addition  to 
these,  there  are  some  cells  that  possess  large  bodies  and 
few  processes.  Fibres  that,  apparently,  have  no  connection 
with  any  cell  are  seen  passing  over  or  under  cell  bodies. 
These  processes  all  interlace  to  form  a  network  for  the  sup- 
port of  the  nerve  cells  and  their  processes.  This  substance 
is  the  SUBSTANTIA  SPONGIOSA.  Around  the  central  canal  of 
the  cord,  the  subs  tan  tia  spongiosa  becomes  more  modified, 
and  is  called  the  SUBSTANTIA  GELATINOSA  CENTRALIS.  The 
network  is  much  closer  in  this  region.  Around  the  dorsal 
horns,  it  forms  a  homogeneous,  striated  mass,  in  which  a  few 
nerve  cells  are  found.  This  is  the  SUBSTANTIA  GELATINOSA 

ROLANDI,   CAPUT  GLIOSIUM,  Or  GLIOSA  CORNUALIS. 

The  WHITE  SUBSTANCE  consists  of  myelinated  nerve 
fibers,  connective  tissue,  and  neuroglia.  Spider  cells  are 
especially  numerous  here.  The  nerve  fibres  possess  no 
neurilemma,  and  are  grouped  into  columns.  Ventrally,  they 
are  separated  by  the  fissure,  and  dorsally,  by  the  septum, 
into  the  hemispheres.  Ventrally,  they  are  connected  by  a 
band  of  white  substance  that  lies  between  the  bottom  of  the 
fissure  and  the  gray  commissure.  This  is  the  WHITE,  or 
VENTRAL  (ANTERIOR)  commissure.  The  MOTOR  fibres  are 
usually  large,  measuring  15  to  20  microns  in  diameter. 
The  SENSOR  are  smaller. 

The  following  columns  are  not  found  in  any  one  section 
of  the  cord  but  represent  all  that  are  definitely  bounded. 
Fig.  89  represents  merely  a  diagramatic  section  locating  all 
the  columns. 

The  VENTRO-MEDIUM  columns  that  lie  between  the 
ventro-median  fissure  and  the  ventral  roots  of  the  spinal 
nerves;  the  LATERAL,  that  lie  between  the  ventral  and 
dorsal  roots,  and  are  subdivided  into  VENTRO-LATERAL,  or 
those  ventral  to  the  transverse  midline,  and  the  DORSO- 
LATERAL,  or  those  behind  the  same  line.  The  DORSO- 


THE    SPINAL    CORD.  269 

MEDIAN  columns  lie   between  the  septum  and  the  dorsal 
roots  of  the  spinal  nerves,  subdivided  into   DORSO-INTER- 

NAL  and   DORSO-EXTERNAL. 

These  areas  are  further  subdivided  into  individual 
columns.  In  the  VENTRO-MEDIAN  region,  there  are  several 
groups :  i .  the  DIRECT  PYRAMIDAL  TRACT  (TURCK)  .  This  is 
a  narrow  band  of  fibres  that  lies  along  the  fissure,  and 
represents  the  nondecussating  fibres  from  the  motor  regions 
of  the  brain.  The  bundle  lies  next  to  fissure  in  thoracic 
region  and  disappears  in  the  lumbar  part  of  the  cord. 
A  descending  tract. 

2 .  The  SULCO-M ARGINAL  TRACT  is  f  ound  only  in  the  cervical 
part  of  the  cord  and  consists  of  fibres  from  opposite  quadri- 
gemina  and  represents  a  descending  tract.     It  lies  next  to  the 
fissure. 

3.  The  VENTRAL  VESTIBULO-SPINAL  TRACT  (Loewen thai' s) 
lies  at  ventral  surface  of  the  cord  in  cervical  and  thoracic 
portions  and  consists  of  descending  fibres. 

4.  VENTRAL  GROUND  BUNDLE.    This  consists  of  fibres  that 
arise  in  the  cord  and  end  in  the  cord,  extending  up  and 
down  for  short  distances  in  order  to  connect  the  various 
segments    of    the    cord.     These    fibres    are    associative    in 
function. 

In  the  LATERAL  region  of  the  cord  are  the  following  tracts : 

1.  SUPERFICIAL  VENTRO-LATERAL,  or  SPINO-CEREBELLAR 
(GOWERS)  lies  in  the  superficial  ventral  portion  of  the  lateral 
area.     The  fibres  probably  arise  from  cells  on  both  sides 
of   cord    in  visceral   and   partly   ventral   regions   and    are 
ascending. 

2.  SPINO-OLIVARY,  or  HELWEG'S  TRACT,  lies  just  lateral 
to  the  ventral  root  and  is  found  only  in  cervical  and  upper 
thoracic   portions   of    the   cord    and    represents   ascending 
fibres. 

3.  DIRECT  SPINO-CEREBELLAR  TRACT  lies  in  the  superficial 


270  TIIK    NERVE    SYSTKM. 

dorso-lateral  area  and  consists  of  ascending  fibres  from  the 
cells  of  the  column  of  Clark.  This  tract  is  not  found  in  the 
lower  lumbar  region  of  the  cord. 

4.  CROSSED   PYRAMIDAL  TRACT,  is    in    the   dorso-lateral 
region  of   the  cord  and  is  composed  of  fibres  that  descend. 
In  the  cervical  region  it  is  internal  to  the  direct  cerebellar 
tract  but  in  the  thoracic  area  of  the  cord  it  comes  partially 
to  the  surface,  and  in  the  lumbar  region,  where  the  direct 
cerebellar    tract    is    absent,  the    crossed    pyramidal    tract 
lies  entirely  superficial. 

5.  LATERAL  GROUND  BUNDLE  lies  against  the  gray  sub- 
stance and  consists  of  associative  fibres  of  both  descending 
and  ascending  courses. 

6.  LATERAL  MIXED  TRACT  occupies  the  remainder  of  the 
lateral  columns  and  in  it  several  tracts  have  been  more  or 
less  completely  outlined  as  follows  (see  Fig.  89) : 

a.  RUBRO-SPINAL,  descending. 

b.  CEREBELLO-SPINAL,  descending. 

c.  Lateral  VESTIBULO-SPINAL,  descending. 

d.  OLIVO-SPINAL,  descending. 

These    collectively    are    also     termed    the    FASCICULUS 

INTERMEDIUS. 

In  the  DORSAL  region  are  seen  the  following  tracts  : 

1.  FASCICULUS  GRACILIS  (COLUMN  OF  GOLL)  lies  adjacent 
to    the   dorso-median    septum    and    consists  of    ascending 
fibres  that  arise  in  the  cells  of  the  spinal  ganglia  (the  axonic 
processes).     These  fibres  end  in  the  nucleus  gracilis. 

2.  FASCICULUS   CUNEATUS    (COLUMN  OF    BURDACH)  lies 
peripheral  to  the  preceding,  and  likewise  consists  of  fibres 
(axones  derived  from  the  cells  of  the  spinal  ganglia  that 
ascend). 

3.  The  DORSAL  GROUND  BUNDLE  lies  next   to   the  gray 
substance  of  the  dorsal  horn  and  consists  of  short  fibres  that 
ascend  and  descend;  they  are  associative  in  function. 


THE    SPINAL    CORD.  271 

4.  The  COMMA  TRACT  of  SCHUTZE  occupies  a  position  in 
the  tract  of  Burdach  at  the  boundary  line  with  the  tract  of 
Goll.     Its  fibres  are  descending. 

5.  The     MARGINAL     TRACT,     Or     TRACT     OF     SPITZKA,     Or 

LISSAUER,  is  located  along  the  dorsal  root  or  among  its 
fibres.  It  consists  of  some  of  the  axones,  of  cells  of  the 
spinal  ganglia,  which  traverse  not  more  than  three  or  four 
segments  and  end  around  the  cells  in  the  gliosa  cornualis. 
It  is  sensor  in  function  and  is  probably  concerned  with 
transmission  of  pain  sense.  All  of  the  above  tracts  are 
found  in  all  levels  of  the  cord. 

6.  The  DORSAL  CORNUCOMMISSURAL  TRACT  is  associative 
in  function,  consisting  of    both  ascending  and  descending 
fibres. 

7.  The    SEPTOMARGINAL     TRACT     (Bruce)    consists    also 
associative  in  function  and  lies  along  the  postseptum.     Its 
fibres  ascend  and  descend.      Both  of  these  tracts  are  most 
distinct  in  the  lumbar  region  of  the  cord. 

The  gray  substance  of  the  cord  can  be  subdivided 
functionally  into  the  following  categories:  i.  SOMATO- 
MOTOR;  2.  VISCERO-MOTOR;  3.  VISCERO-SENSOR;  4.  SOMATO- 
SENSOR,  as  shown  in  Fig.  91.  The  course  of  the  various 
components  of  the  nerve-roots  is  likewise  shown. 

The  SPINAL  NERVES  Consist  Of  VENTRAL,  MOTOR,  Or 
EFFERENT,  and  DORSAL,  SENSOR,  Or  AFFERENT  ROOTS. 

Before  these  unite  to  form  the  nerve,  a  mass  of  gray 
substance  is  seen  upon  the  dorsal  root.  This  is  the  SPINAL 
GANGLION.  The  fibres  of  the  DORSAL  ROOT  are  derived  from 
the  cells  that  lie  in  the  ganglia,  and  where  they  enter  the 
cord,  a  distinct  depression  is  noted.  The  fibres  peripheral 
to  the  ganglion  represent  myelinated  dendrites  and  those 
that  enter  the  dorsal  root  of  the  spinal  cord  represent  the 
myelinated  axones.  Upon  examining  Fig.  91  it  will  be 
that  the  dorsal  root  is  not  purely  sensor,  but  also  con- 


272 


THE   NERVE    SYSTEM. 


tains  mscero -motor  fibres.  The  VENTRAL  ROOT  is  made  up 
of  fibres  derived  from  the  cells  in  the  ventral  horn,  and 
where  they  emerge  only  a  slight  incurving  of  the  surface  is 
seen. 

The  circulation  of  the  nerve  system  is  carried  on  chiefly 
by  the  vessels  in  the  pia.     In  the  CEREBRUM,  the  vessels  of 


FIG.  91. — A  DIAGRAM  OF  THE  COUPON  KM    ELEMENTS  OF  THE  SPINAL 

CORD  AND  ITS  NERVE-ROOTS  IN  A  TRUNK-SEGMENT  ILLUSTRATING 

THE  FOUR  FUNCTIONAL  DIVISIONS  OF  THE  NERVE  SYSTEM. 

(After  Johnston.} 

ss,  Somatic  sensor;  vs,  visceral  sensor;  VM,  visceral  motor;  SM,  somatic 
motor.  The  arrow  heads  indicate  the  directions  of  the  impulses.  Note 
that  visceral  motor  impulse  passes  out  through  the  dorsal  root. 

the  cortex  enter  vertically,  and  form  a  close  plexus  of 
capillaries  most  plentiful  where  the  cells  are.  Those  in- 
tended for  the  medulla  are  larger,  and,  passing  through  the 
cortex,  form  capillary  networks  between  the  fibres  and 
parallel  to  them. 

In  the  CEREBELLUM,  the  capillaries  are  few  in  the  outer 


THE    SPINAL    CORD.  273 

portion  of  the  molecular  layer,  but  in  the  granule  layer  and 
around  the  cells  of  Purkinje,  close  meshes  are  formed. 

In  the  SPINAL  CORD,  there  are  two  sets  of  vessels,  those 
that  enter  at  all  points  of  the  periphery  and  supply  chiefly 
the  white  matter,  and  those  derived  from  the  artery  lying 
in  the  ventro-median  fissure;  the  latter  set  goes  to  the  gray 
substance.  The  smaller  peripheral  vessels  remain  in  the 
white  substance,  and  run  parallel  to  the  fibres,  while  the 
larger  penetrate  the  gray  substance  and  supply  the  outer 
part.  The  artery  in  the  fissure  sends  branches  into  the  gray 
commissure;  these  divide  right  and  left,  and  form  dense 
plexuses  in  the  gray  substance. 

The  blood  is  collected  by  venous  radicals  that  have  the 
same  general  course. 

The  SUBARACHNOIDEAN  LYMPH  SPACE  continues  as  the 
PERIVASCULAR  LYMPHATICS  that  accompany  the  blood- 
vessels. 


18 


CHAPTER  XVIII. 

THE  EYEBALL  AND  LACRIMAL  SYSTEM. 

The  Eyeball  is  one  of  the  most  important  organs  of  the 
special  senses.  It  is  composed  of  THREE  COATS,  and  contains 
FOUR  REFRACTIVE  MEDIA.  The  COATS  are  the  External,  or 
Corneo-sclera;  the  Middle,  or  Choroid,  Ciliary  Body  and 
Iris ;  and  the  Internal,  or  Retina. 

The  REFRACTIVE  MEDIA  are  the  CORNEA,  the  AQUEOUS 
and  VITREOUS  HUMORS  and  the  LENS.  Of  these,  the  cornea 
and  lens  alone  are  of  importance. 

The  Corneo-sclera  is  the  protective  and  transparent  coat 
of  the  eyeball. 

The  Sclera  constitutes  about  five-sixths  of  this  coat.  It 
is  composed  of  coarse  bundles  of  white  fibrous  tissue  that 
interlace  to  form  a  dense,  tough  coat.  These  bundles  are 
arranged  chiefly  longitudinally  and  transversely.  Between 
the  bundles  are  spaces  that  contain  large,  stellate  cells. 
These  spaces  communicate  with  the  lymph  spaces  within  the 
cornea.  On  its  external  surface,  the  sclera  is  in  relation 
with  the  CAPSULE  OF  TENON,  and,  anteriorly,  the  CON- 
JUNCTIVA. To  it  are  attached  the  ocular  muscles. 

Between  the  sclera  and  choroid  is  a  lymph  space  called 
the  SUBSCLERAL  SPACE.  Here  the  tissue  is  loosely  arranged 
and  lined  by  endothelial  cells.  At  the  exit  of  the  optic 
nerve,  the  sclera  is  pierced  by  the  nerve  fibres  so  as  to  form 
a  sieve-like  area,  the  LAMINA  CRIBROSA.  Pigmentation  oc- 
curs here,  as  well  as  at  the  corneo-scleral  junction.  Its 
presence  in  the  subscleral  tissue  gives  rise  to  the  LAMINA 
FUSCA. 

274 


THK   CORNEA.  275 

The  Cornea  is  a  specialized  portion  of  the  sclera  modified 
for  the  transmission  of  light.  It  consists  of  FIVE  LAYERS: 

ANTERIOR  EPITHELIUM,  ANTERIOR  LIMITING  MEMBRANE, 
SUBSTANTIA  PROPRIA,  POSTERIOR  LIMITING  MEMBRANE,  and 
POSTERIOR  ENDOTHELIUM. 

The  ANTERIOR  EPITHELIUM  is  a  continuation  of  the  epi- 
thelium of  the  conjunctiva.  This  is  of  the  stratified  squam- 
ous  variety,  and  the  tunica  propria  beneath  is  not  papillated. 
The  layers  of  cells  are  more  numerous  at  the  corneo-scleral 
junction  than  in  the  center.  The  basal  cells  are  long  and 
columnar,  and  possess  processes  that  extend  into  the  an- 
terior elastic  lamina,  while  the  external  cells  are  squamous. 
The  middle  layers  are  prickle-cells,  and  the  spaces  between 
are  lymph  channels. 

The  ANTERIOR  ELASTIC  LAMINA,  or  BOWMAN'S  MEMBRANE, 

is  a  clear,  prominent  band  serving  as  a  basement  membrane 
to  the  epithelial  cells.  Although  called  elastic,  it  does  not 
consist  of  elastic  tissue.  It  is  thickest  in  the  center,  and 
becomes  thinner  as  the  junction  is  approached,  where  it 
disappears  entirely. 

The  SUBSTANTIA  PROPRIA  forms  the  bulk  of  the  cornea, 
and  consists  of  a  number  of  layers  (about  sixty)  of  white 
fibrous  tissue  arranged  parallel  to  one  another.  It  is  due  to 
this  arrangement  that  this  organ  is  transparent.  In  addi- 
tion to  these  fibres,  there  are  others  that  penetrate  the  organ 
at  a  right  angle  to  the  layers,  and  bind  all  together.  These 
are  the  perforating  fibres.  Between  the  various  layers  are 
a  large  number  of  irregular  spaces  called  the  CORNEAL  LA- 
CUNA. These  contain  large  stellate  cells  that  are  the 
original  connective-tissue  cells  of  the  organ.  They  are  the 
CORNEAL  CORPUSCLES.  The  spaces  communicate  with  one 
another  by  means  of  little  canals  called  CANALICULI,  into 
which  their  processes  extend.  These  spaces  are  readily 
shown  by  the  gold  chlorid  method  of  staining. 


276  THE   EYEBALL  AND    LACRIMAL    SYSTEM. 

The   POSTERIOR    LIMITING    MEMBRANE,    OF    MEMBRANE   OF 

DESCEMET,  is  analogous  to  the  anterior  membrane;  unlike 
this  one,  however,  it  is  thicker  peripherally  than  centrally, 
and  seems  more  independent  of  the  substantia  propria  than 
the  anterior.  It  does  not  respond  to  the  elastica  stain,  and, 
consequently,  is  not  made  up  of  elastic  tissue,  as  its  name 
would  seem  to  indicate.  It  becomes  the  pectinate  ligament. 

The  ENDOTHELIAL  LAYER  consists  of  a  single  layer  of  well- 
defined  regular  cells,  which  cover  the  posterior  surface  of 
this  organ,  and  continues  over  the  anterior  surface  of  the 
iris.  These  cells  are  hexagonal,  and  possess  a  fibrillar 
protoplasm  that  seems  to  extend  through  several  layers. 

The  cornea  possesses  blood-vessels  during  the  develop- 
mental period;  these,  however,  disappear  before  birth,  so 
that  none  are  then  present.  Lymph,  which  circulates 
through  the  many  spaces  and  canaliculi,  nourishes  the 
cornea. 

The  sclera  possesses  but  few  vessels,  and  these  are  found 
chiefly  at  the  corneo-scleral  junction,  where  a  circular  net- 
work is  formed. 

The  nerves  are  SENSOR;  at  the  corneo-scleral  junction  a 
circular  plexus  is  formed,  from  which  fibres  pass  into  the 
substantia  propria,  while  others  penetrate  the  anterior 
elastic  lamina  to  pass  into  the  epithelial  layer.  Some  of 
these  fibres  extend  almost  to  the  surface. 

The  Middle  Coat,  or  tunic,  also  called  the  Uveal  Tract, 
is  the  vascular  coat.  It  contains  the  main  vessels  of  the 
eyeball,  except  the  central  artery  of  the  retina,  and  consists 
of  the  Choroid,  Ciliary  Body  and  Iris. 

The  Choroid  is  the  vascular  portion,  and  is  divided  into 
three  layers,  the  STROMA  LAYER,  the  CHORIO-CAPILLARIS, 
and  the  GLASSY  MEMBRANE,  from  without,  inward. 

The  STROMA  LAYER  is  sometimes  referred  to  as  the  layer 
of  large  vessels,  as  they  are  found  only  in  this  portion.  It 


THE    CHOROID. 


277 


consists,  externally,  of  delicate  fibres  that  connect  with 
those  of  the  subscleral  tissue  and  form  a  complete  space,  the 

SUPRACHOROIDAL,    Or    SUBSCLERAL    LYMPH    SPACE.       In    this 

tissue  are  found  pigmented  connective-tissue  cells,  and  it  has 
received  the  name  of  LAMINA  SUPRACHOROIDEA.  The  main 
portion  of  the  stroma  layer  consists  of  bundles  that  are 
closely  arranged.  The  network  formed  by  these  are  the 


FlG.  92. — CORNEO-SCLERAL  JUNCTION  OF  MAN. 

i.  Epithelium;  2.  connective  tissue  of  conjunctiva;  3.  sclera;  4,  5,  6,  7  and  8. 
ciliary  body;  4.  meridional;  5.  radial;  6.  circular  fibres  of  ciliary  muscle; 
7.  ciliary  process;  8.  pars  ciliaris  retinae;  9.  pars  iridica  retinae;  10. 
stroma  of  iris;  n.  posterior  elastic  lamina  of  cornea;  12.  substantia 
propria;  13.  epithelium;  14.  canal  of  Schlemm;  15.  angle  of  iris,  or 
infiltration  angle  (Stohr's  Histology). 

-venous  trunks,  externally,  and  the  arterial  trunks,  internally; 
the  latter  are  accompanied  by  bundles  of  smooth  muscle 
tissue.  Pigmented  cells  exist  between  the  bundles. 

The  inner  portion  of  this  layer  is  called  the  BOUNDARY 
ZONE;  the  bundles  are  arranged  into  several  layers  in  her- 
bivorous animals,  so  as  to  give  a  peculiar  metallic  reflex,  and 
constitutes  the  TAPETUM  FIBROSUM.  This  area  is  usually 


278  THE   EYEBALL   AND   LACRIMAL    SYSTEM. 

free  from  pigment  cells.  In  the  carnivorous  animals  t la- 
fibres  are  replaced  by  distinct  cells  that  contain  crystals. 
The  metallic  reflex,  however,  is  the  same.  This' forms  the 

TAPETUM  CELLULOSUM. 

The  CHORIO-CAPILLARIS  contains  little  stroma,  and  is 
composed  chiefly  of  a  dense  capillary  plexus.  No  pigment 
cells  are  seen.  The  capillaries  are  most  numerous  around 
the  macula  latea. 

The  GLASSY  MEMBRANE  lies  at  the  inner  boundary  of  the 
choroid,  and  consists  of  refractile,  homogeneous  tissue.  It 
is  a  very  thick  basement  membrane,  and  supports  the  pig- 
mented  cells  of  the  retina. 

The  choroid  extends  to  the  ORA  SERRATA,  a  peculiar, 
serrated  line,  at  which  the  neural  portion  of  the  retina 
ceases.  At  this  point,  the  choroid  continues  as  the  Ciliary 
Body. 

The  Ciliary  Body  is  composed  of  three  main  portions, 
the  Ciliary  Ring,  the  Ciliary  Processes  and  the  Ciliary  Muscle. 
It  is  thicker  than  the  choroid,  which  is  due  especially  to  the 
addition  of  the  muscle  tissue. 

The  Ciliary  Ring  is  practically  the  continuation  of  the 
stroma  layer  of  the  choroid  and  the  boundary  membrane, 
and  consists  of  dense  white  fibrous  tissue,  which  forms  a 
circular  band  about  4  mm.  in  breadth.  The  vessels  have  a 
longitudinal  course. 

The  Ciliary  Processes  are  projections  of  the  stroma, 
covered  by  pigmented  epithelial  cells,  from  60  to  80  in 
number.  They  arise  at  the  junction  with  the  choroid,  and 
extend  toward  the  iris,  increasing  in  height,  ending  abruptly 
at  that  point.  At  this  place  they  are  about  i  mm.  in  height. 
Each  process  consists  of  a  core  of  stroma  (connective  tissue) 
supporting  blood-vessels  and  covered  by  the  pigmented 
epithelial  cells  of  the  retina,  the  PARS  CILIARIS  RETINA. 
These  cells  rest  upon  a  continuation  of  the  glassy  mem- 


THE    CILIARY    MUSCLE.  279 

brane.  There  are  two  layers,  the  outer,  or  basal  of  which 
consists  of  low  columnar  or  cuboidal  elements  that  are  the 
continuation  of  the  true  pigmented  cells  of  the  retina.  The 
inner  layer  is  composed  of  cells  that  are  columnar,  possess 
little  or  no  pigment,  and  are  the  representative  of  the 
optical  portion  of  the  retina. 

The  Ciliary  Muscle  is  of  the  nonstriated  variety,  and  lies 
external  to  the  ciliary  ring,  just  beneath  the  sclera.  The 
fibres  are  arranged  in  MERIDIONAL,  RADIAL  and  CIRCULAR 
sets.  The  MERIDIONAL  are  the  outermost,  and  extend  from 
the  canal  of  Schlemm,  in  the  corneo-scleral  junction,  to  the 
ciliary  ring.  These  are  the  tensor  muscles  of  the  choroid. 
The  RADIAL  fibres,  which  compose  the  middle  layer,  extend 
peripherally,  and,  spreading  fan-like,  are  inserted  into  the 
ciliary  ring  and  processes.  The  CIRCULAR  fibres  are  the 
inner  ones,  and  their  direction  is  equatorial.  They  consti- 
tute MUELLER'S  RING-MUSCLE. 

The  ciliary  region  is  indicated,  externally,  by  a  band 
about  one-fourth  of  an  inch  broad,  starting  at  the  corneo- 
scleral  junction.  It  is  called  the  danger  zone  of  the  eyeball, 
as  injuries  here  usually  result  fatally  to  sight. 

The  Iris  is  the  continuation  of  the  stroma  layer  and  glassy 
membrane  of  the  choroid.  It  receives  also  the  posterior 
lamina  and  the  endothelium  of  the  cornea,  and  consists  of 

the  ANTERIOR  ENDOTHELIUM,  STROMA  LAYER,  POSTERIOR 
LAMINA  and  PIGMENT  LAYERS. 

The  ANTERIOR  ENDOTHELIUM  is  a  continuation  of  that  of 
the  cornea,  and  covers  the  anterior  surface  of  the  iris.  The 
cells  are  neither  so  regular  nor  distinct  as  those  of  the 
cornea. 

The  STROMA  LAYER  is  composed  chiefly  of  a  coarse  net- 
work of  white  fibrous  tissue,  some  of  which  is  circularly 
arranged  around  the  blood-vessels,  which  possess  no  muscu- 
lar coat.  Anteriorly,  this  stroma  is  very  much  reticulated 


280  THE   EYEBALL   AND    LACRIMAL    SYSTEM. 

and  forms  a  support  for  the  endothelial  cells.  According 
to  some  authors,  this  portion  constitutes  an  anterior  limiting 
membrane.  In  the  stroma  layer,  pigment  cells  are  found  in 
varying  quantities;  in  gray  eyes,  very  few  are  seen;  as  the 
color  passes  to  blue,  brown  and  black,  the  number  increases, 
the  last  possessing  the  most.  In  albino  eyes  not  only  are 
the  pigmented  connective  cells  of  the  stroma  layer  absent, 
but  the  pigment  that  is  usually  present  in  the  posterior 
epithelial  cells  continued  from  the  retina  is  also  absent. 
As  a  result  of  this,  the  retinal  blood-vessels  cause  a  peculiar 
red  reflex,  the  retinal  reflex.  In  the  other  eyes  the  pigment 
obscures  it. 

In  the  stroma,  is  found  muscle  tissue  of  the  involuntary 
nonstriated  variety.  This  is  arranged  CIRCULARLY  and 
RADIALLY.  The  CIRCULAR  fibres  are  near  the  anterior  part 
of  the  iris,  and  contract  the  pupil  when  stimulated;  these 
form  the  SPHINCTER  PUPILL^  muscle.  The  RADIAL  fibres 
lie  near  the  posterior  part,  and  when  they  contract,  the 
pupil  is  dilated;  they  constitute  the  DILATOR  PUPILL^ 
muscle. 

The    POSTERIOR    LIMITING    MEMBRANE,    or    MEMBRANE    OF 

BRUCH,  is  a  continuation  of  the  glassy  membrane.  It  sup- 
ports the  pigmented  cells,  the  PARS  IRIDICA  RETINA. 

The  PIGMENTED  LAYER,  a  continuation  of  the  pars  ciliaris 
retinae,  and  called  the  PARS  IRIDICA  RETINA,  is  usually 
pigmented,  and  consists  of  two  layers  of  cells.  It  continues 
to  the  anterior  margin  of  the  pupil. 

The  PUPIL  is  the  aperture  in  the  iris.  Its  size  is  regulated 
automatically  by  the  amount  of  light  entering. 

The  Corneo-scleral  junction  is  the  region  in  which  cornea, 
sclera,  ciliary  body  and  iris  come  together.  The  sclera 
passes  over  into  the  cornea,  but  the  line  of  transition  is  not 
abrupt,  but  gradual,  and  forms  an  oblique  line  that  extends 
from  before,  backward  and  inward.  Beneath  the  posterior 


THE    RETINA.  .  281 

margin,  usually  within  the  sclera,  is  a  circidar  canal,  the 
CANAL  OF  SCHLEMM,  which  extends  around  the  corneo- 
scleral  junction.  In  this  region,  the  membrane  of  Descemet 
is  seen  to  divide  into  a  large  number  of  fibres  that  extend 
to  the  base  of  the  iris.  Between  the  fibres  are  found 
many  intercommunicating  spaces  called  the  SPACES  OF 
FONTANA.  These  spaces  lie  around  the  angle  formed  by 
the  cornea  and  iris,  called  the  INFILTRATION  ANGLE,  and 
communicate  with  the  anterior  chamber  and  the  canal  of 
Schlemm.  The  network  is  called  the  PECTINATE  LIGAMENT, 
and  is  covered  by  endothelial  cells. 

THE  RETINA. 

The  Retina  forms  the  INTERNAL,  or  NEURAL  COAT  of  the 
eyeball.  It  may  be  divided  into  two  portions,  the  PARS 
OPTICA,  that  portion  capable  of  vision,  and  the  PARS  CECA, 
or  the  blind  part,  possessing  no  nerve  elements.  The 
latter  portion  is  further  subdivided  into  PARS  CILIARIS  and 
PARS  IRIDICA  RETINA.  The  simplest  division  of  the  retina, 
however,  is  PARS  OPTICA,  PARS  CILIARIS  and  PARS  IRIDICA 
RETIN/E. 

The  PARS  OPTICA  lines  almost  the  entire  optic  cup,  and 
extends  forward  to  the  end  of  the  choroid.  Here  the  neu- 
ral portion  ceases,  and  the  coat  becomes  abruptly  thinner, 
and  forms  an  irregular  serrated  line,  the  ORA  SERRATA. 
From  this  point,  the  last  two  portions  of  the  retina  continue. 

The  optical  portion  consists  of  eleven  layers,  counting  the 
pigmented  layer.  These  layers  are  classed  as  NEURO-EPI- 

THELIAL    and    CEREBRAL.       The    NEURO-EPITHELIAL    portion 

consists  of  the  first  five  layers  within  the  pigment  layer,  and 
the  CEREBRAL  portion  the  remaining  divisions.  The  pig- 
mented part  is  derived  from  the  outer  layer  of  the  optic 
cup,  and  the  other  parts  from  the  inner  layer. 


282  THE   EYEBALL  AND    LACRIMAL    SYSTEM. 

Optic  Vesicle.         Retinal  Layer.  Classes. 

1.  Outer  Layer.    PIGMENTED  LAYER  .    .    .  PIGMENT  LAYER. 

f  LAYER  OF  RODS  AND  CONES. 
I  EXTERNAL  LIMITING 

MEMBRANE    ....  NEURO-EPITHELIAL 

LAYER. 

OUTER  GRANULAR  LAYER. 
HENLE'S  FIBRE  LAYER. 

2.  Inner  Layer  \  OUTER  RETICULAR  (MOLECULAR). 

OUTER  GANGLIONIC  (INNER  GRANULE). 
INNER  RETICULAR 

(MOLECULAR) CEREBRAL. 

INNER  GANGLIONIC. 

NERVE  FIBRES. 

INTERNAL  LIMITING  MEMBRANE. 

1.  The  PIGMENT  LAYER  consists  of  polyhedral  cells  con- 
taining a  black,  granular,  mobile  pigment.     The  position 
occupied  by  this  pigment  depends  upon  the  presence  or 
absence  of  the  light.     The  nonpigmented  nuclei  occupy  the 
basal  portion  of  the  cells.     These  cells  continue  over  the 
ciliary  body  and  iris  as  the  PARS  CILI  ARIS  and  IRIDICA  RETINA. 
In  the  iris,  both  layers  are  pigmented,  but  not  in  the  ciliary 
region.     This  layer  is  derived  from  the  outer  layer  of  the 
optic  cup. 

The  nerve  structures  are  supported  by  NEUROGLIA,  of 
which  a  great  deal  is  present  and  unevenly  distributed. 

2.  The  LAYER  OF  RODS  AND  CONES  is  the  most  important 
portion  of  the  retina. 

The  CONES  consist  of  CELL-BODY  and  CONE-FIBRE.  The 
CELL-BODY  is  about  30  microns  in  length,  and  is  divided  into 
two  segments,  outer  and  inner.  The  outer  is  conical,  may 
be  striated,  rests  upon  the  limiting  membrane,  and  is  ap- 
parently composed  of  discs.  The  inner  segment  is  striated 
and  flask-shaped.  At  its  junction  with  the  outer  segment, 
it  is  granular,  and  the  other  part  is  fibrillar.  The  cone-fibre 


THE    RETINA. 


283 


ends  in  the  outer  reticular  layer,  and  has  a  nucleus  near  its 
junction  with  the  body. 


c 


H 


FIG.  93. — SECTION  OF  HUMAN  RETINA  (after  Pier  sol). 

A,  Part  of  pigment  layer;  B,  layer  of  rods  and  cones;  C,  external  limiting 
membrane;  D,  (outer)  nuclear  layer;  E,  outer  reticular  layer;  F,  outer 
ganglionic  layer;  G,  inner  reticular  layer;  H,  inner  ganglionic  layer; 
7,  layer  of  nerve  fibers;  K,  inner  limiting  membrane.  Henle's  fiber- 
layer  is  not  represented. 

The  RODS  are  longer  than  the  cones,  averaging  about  50 
microns.  They  have  somewhat  the  same  structure  as  the 
preceding  and  are  almost  uniform  in  size.  The  different 


284  THE    EYEBALL   AND    LACRIMAL    SYSTEM. 

segments  react  differently  to  stains.  The  outer  segment 
possesses  prominent  cross  and  faint  longitudinal  striations. 
In  this  portion  of  the  cell,  the  RHODOPSIN,  or  VISUAL 
PURPLE,  is  located.  The  inner  segment  is  spindle-shaped, 
granular,  and  fibrillar  like  the  above.  The  rod  fibres 
terminate  in  the  outer  reticular  layer,  where  they  are  en- 
larged. The  nuclei  lie  in  the  outer  granular  layer.  They 
may  be  irregularly  placed,  and  in  lower  animals  may  even 
be  striated. 

Usually  three  or  four  rods  are  seen  to  each  cone.  In 
the  central  portion  of  the  yellow  spot  the  cones  alone  are 
present. 

3.  The    EXTERNAL    LIMITING    MEMBRANE    Consists    of    the 

outer  ends  of  the  fibres  of  Miiller.  These  run  radially,  and 
extend  through  almost  the  entire  thickness  of  the  retina. 
The  outer  ends  of  these  fibres  are  enlarged,  and  lie  so  close 
together  that  they  form  a  membrane,  the  OUTER  LIMITING 
MEMBRANE.  These  fibres  do  not  penetrate  the  rod  and  cone 
layer,  but  give  branches  to  all  of  the  other  layers.  Each 
fibre  possesses  a  nucleus  that  lies  in  the  inner  nuclear  layer. 
At  their  internal  ends,  they  are  again  enlarged,  and  form 
the  INTERNAL  LIMITING  MEMBRANE.  Glia  cells  are  also 
present. 

4.  The  GRANULE,  or  NUCLEAR  LAYER  consists  of  several 
layers  of  oval  nuclei,  which  are  the  granules.     These  are 
the  nuclei  of  the  rod  and  cone-fibres.     The  former  are  the 
more  numerous. 

5.  HENLE'S  FIBRE  LAYER  is  best  developed  in  the  macular 
region,  from  which  area  it  diminishes  peripherally.     It  is 
made  up  of  the  inner  segments  of  the  red  and  cone-fibres. 

6.  The  OUTER  MOLECULAR,   Or  RETICULAR  LAYER  is  COm- 

posed  of  the  inner  ends  of  the  rod  and  cone  cells,  which  are 
branched,  and  fibrillar,  and  proceed  from  the  inner  nuclear 
layer. 


THE    RETINA.  285 

7.    The  OUTER  GANGLIONIC,  Of  INNER  GRANULAR  LAYER  is 

made  up  of  several  varieties  of  closely  packed  cells,  the 
most  numerous  of  which  are  OVAL,  BIPOLAR  ELEMENTS. 
These  are  placed  vertically,  and  the  small  amount  of  proto- 
plasm present  continues  as  an  inner  process  that  passes  to 
the  inner  molecular  layer;  here  it  breaks  into  many  branches 
that  form  a  network  around  the  ganglion  cells.  The  outer 
processes  of  these  oval  cells  surround  the  ends  of  the  rod- 
fibres  in  the  form  of  a  delicate  rete,  or  mesh  of  fibrillae. 


-f 


t 


FIG.  94. — CELLS  FROM  RETINA  OF  AN  APE  (Stohr's  Histology}. 
i.  Cell  of  ganglionic  of  layer.  2.  Cells  of  inner  granule  layer.  3.  Rod- 
cells:  a.  outer  egment;  b.  inner  segment;  k.  rod-granule;  x.  fibre  appara- 
tus. Below  are  rod-cells  and  fragments.  4.  Cone-visual  cells:  a.  outer 
segment;  i.  inner  segment;  k.  cone-granule;/,  cone-fibre;  x.  fibre  appa- 
ratus; 5.  Radial  fibre,  Muller's  fibre:  k.  nucleus;  r.  pyramidal  base. 


Other  cell-processes  pass  to  the  cone-fibres  and  to  the  inner 
molecular  layer. 

Another  kind  of  cell  is  present,  the  AMAKRINE  CELL, 
which  forms  a  layer  near  the  inner  boundary  of  this  nuclear 
layer.  These  cells  possess  no  axis  cylinders,  but  other 
processes  extend  into  the  inner  molecular  layer. 

A  third  variety  possesses  a  cell-body,  the  long  diameter 
of  which  lies  parallel  to  the  surface  of  the  retina.  The  proc- 
esses pass  into  the  outer  molecular  layer.  Some  connect 
with  the  rod-fibres;  these  are  larger  and  lie  internally, 


286  THE    EYEBALL  AND    LACRIMAL    SYSTEM. 

while  the  others  that  pass  to  the  cone-fibres  are  smaller  and 
have  an  external  position. 

In  addition  to  the  above,  there  are  some  cells  present  in 
this  layer  that  send  their  axis  cylinders  into  the  optic 
nerve. 

The  nuclei  of  Miiller's  fibres  lie  in  this  layer. 

8.  The  INNER  RETICULAR,  or  MOLECULAR 'LAYER  consists 
of  fibrils  of  cells  of  the  preceding  layer  and  from  cells  of  the 
inner  ganglionic  layers.     The  fibres  lie  at  different  levels, 
which  gives  them  a  striated  appearance. 

9.  The   GANGLIONIC    (INNER)   LAYER    is   composed  of   a 
single  layer  of  multipolar  ganglion  cells.     The  cell-bodies 
are  flask-shaped,  and  the  axis  cylinders  pass  into  the  layers 
of  nerve  fibres.     The  dendritic  processes  extend  into  the 
inner  molecular  layer  at  different  levels,  and,  supposedly, 
do  not  communicate   with   those  of  other  cells.     In   the 
region  of  the  macula  lutea,  these  cells  become  increased  in 
number,  forming,  often,  eight  layers. 

10.  The  LAYER  OF  NERVE  FIBRES  is  the  expanded  optic 
nerve.     These  fibres  pierce  all  the  layers,  except  the  internal 
limiting  membrane.     They  arise,  mainly,  from  the  cells  of 
the  inner  ganglionic  layer,  converge  at  the  blind  spot,  pass 
through  the  cribriform  lamina  of   the  sclera  and   become 
myelinated.     As  most  of  the  fibres  pass  from  the  ganglion 
cells  toward  the  brain,  it  would  be  better  to  say  that  they 
converge  at  the  optic  nerve  exit,  where  the  LAYER  OF  NERVE 
FIBRES  is   thickest,   and  decreases    as    the    ora    serrata  is 
approached. 

11.  The  INTERNAL  LIMITING  MEMBRANE  is  formed  by  the 
fusion  of  the  inner  ends  of  Miiller's  fibres. 

There  are  three  important  areas  in   the  retina:   i.   the 

OPTIC  NERVE  EXIT,  OPTIC  PAPILLA,  or  BLIND  SPOT;  2,  the 
MACULA  LUTEA,  or  YELLOW  SPOT,  and  3,  the  ORA  SERRATA. 

i.  In  the  BLIND  SPOT,  only  the  layer  of  nerve  fibres  is  pres- 


THE    OPTIC    NERVE.  287 

ent.  It  lies  about  one-eighth  of  an  inch  to  the  nasal  side, 
and  about  one-tenth  of  an  inch  below  the  optic  axis.  In 
the  center  is  usually  a  shallow  depression;  around  the  edge 
it  is  raised  and  forms  the  PAPILLA  NERVI  OPTIONS. 

2.  The  YELLOW  SPOT  is  not  in   the  direct  visual  axis. 
The  color  is  due  to  the  presence  of  a  diffuse  yellow  pigment. 
Its  edge  is  raised,  owing  to  the  great  thickness  of  the  inner 
ganglionic  layer.     From    the  edge   to   the  center,    all   the 
layers  decrease  and  disappear,  so  that  in  the  center,  the 
FOVEA    CENTRALIS,    the    cones     alone    are    present.     Here 
vision  is  most  acute. 

3.  At  the  ORA  SERRATA  all  of  the  neural  layers  end  ab- 
ruptly, and  are  continued  as  a  single  layer  of  cuboidal  or 
columnar  cells.     Beyond  this  point,  there  is  no  vision. 

The  light  rays  falling  upon  the  retina  are  not  transmitted 
to  the  brain  by  a  direct  route.  The  impressions  are  re- 
ceived by  the  rods  and  cones,  which  send  impulses  to  the 
outer  reticular  layer;  here  the  impulses  are  received  by  the 
processes  of  the  outer  ganglionic  layer,  conveyed  through 
the  bodies  of  the  cells  of  that  layer  to  the  inner  reticular 
layer;  here  they  are  relayed  to  the  processes  of  the  cells 
of  the  inner  ganglionic  layer  and  to  its  cells  and  thence  to  the 
nerve  fibre  layer;  the  latter  makes  up  the  optic  nerve  by 
means  of  which  the  impulses  are  then  conveyed  to  various 
parts  of  the  brain. 

The  Optic  Nerve  consists  of  a  single  bundle  of  nerve 
fibres  that  possess  no  neurilemmae.  It  is  said  to  contain 
from  450,000  to  800,000  nerve  fibers.  It  is  surrounded  by 
the  dura,  arachnoid,  and  pia,  continued  from  the  brain. 
The  lymph  spaces  included  within  these,  communicate  with 
those  of  the  eyeball.  The  dura  and  pia  pass  over  into  the 
sclera,  but  the  arachnoid,  as  such,  is  lost  before  this  occurs; 
as  a  result,  the  two  lymph  spaces  between  these  three  layers 
become  one.  The  nerve  fibres  penetrate  the  sclera  through 


288  THE    EYKBALL    AM)    LACRIMAL    SYSTEM. 

the  LAMINA  CRIBROSA.  As  they  pass  through  this  coat, 
they  lose  the  myelin  sheath,  so  that  they  become  amyel- 
inated  fibres  when  they  connect  with  the  retina. 

VITREOUS  BODY  AND  LENS. 

Of  the  REFRACTIVE  MEDIA  of  the  eyeball,  the  Vitreous  and 
Aqueous  Humors  and  the  Lens  are  yet  to  be  described. 

The  Vitreous  Humor,  or  Body,  occupies  the  optic  cup, 
or  VITREOUS  CHAMBER.  This  body  consists  of  a  fine 
limiting  membrane,  the  HYALOID  MEMBRANE,  a  delicate 
homogeneous  structure  enclosing  the  substance  of  the 
organ,  which  is  composed  of  about  98  per  cent,  water  and 
2  per  cent,  solid  elements.  The  latter  comprise  connective 
tissue  and  wandering  cells,  and  some  fibrils. 

This  organ  is  traversed  by  a  small  canal,  called  the  CANAL 
OF  STILLING,  or  HYALOID  CANAL.  This  extends  from  the 
optic  nerve  to  the  lens,  and  in  intrauterine  life  is  occupied 
by  a  branch  of  the  retinal  artery,  the  HYALOID  ARTERY, 
that  passes  to  the  lens. 

The  Aqueous  Humor  is  practically  lymph.  It  occupies 
the  anterior  and  posterior  chambers,  and  as  a  refractive 
medium  is  unimportant. 

The  Crystalline  Lens  is  a  solid  body,  and  the  most  im- 
portant refractive  medium  of  the  eyeball.  It  possesses 
two  curvatures,  of  which  the  posterior  is  the  greater.  It  lies 
in  a  depression  of  the  vitreous  humor,  called  the  PATELLAR 
FOSSA,  and  is  held  in  position  by  the  SUSPENSORY 

LIGAMENT. 

The  LENS  consists  of  a  capsule,  within  which  lies  the  lens 
substance.  The  capsule  is  composed  of  delicate  white 
fibrous  tissue,  and  to  it  are  attached  the  ligaments.  This  is 
thicker  anteriorly,  and  seems  composed  of  layers. 

The  SUBSTANCE  OF  THE  LENS  is  of  epithelial  origin,  and 


THE    CHAMBERS    OF    THE    EYEBALL.  289 

consists  of  LENS  FIBRES  that  are  greatly  elongated  cells. 
Upon  the  anterior  surface,  just  beneath  the  capsule,  is  a 
single  layer  of  cuboidal  cells  called  the  LENS  EPITHELIUM. 
At  the  equator  of  the  lens,  these  cells  lengthen,  forming  the 
LENS  FIBRES,  which  are  hexagonal,  nucleated  structures. 
The  nuclei  are  large  and  oval,  and  lie  near  the  middle  of  the 
fibres.  Peripherally,  the  fibres  are  harder  than  those  of  the 
center.  No  cells  are  found  posteriorly. 

The  Suspensory  Ligament  of  the  lens  is  really  a  continua- 
tion of  the  hyaloid  membrane,  reinforced  by  a  large 
number  of  fibres  that  pass  from  the  anterior  and  posterior 
layers  of  the  capsule.  Those  from  the  anterior  layer  pass 
into  depressions  between  the  ciliary  processes,  while  those 
from  the  posterior  layer  are  attached  to  the  summits  of  the 
processes.  Between  these  two  layers  of  fibres  is  a  small 
space,  the  CANAL  OF  PETIT.  This  region  constitutes  the 
ZONE  OF  ZINN. 

The  Chambers  of  the  eyeball  are  Anterior,  Posterior  and 
Vitreous.  The  Anterior  lies  between  the  iris  and  cornea, 
the  Posterior  between  the  lens  and  vitreous  humor,  and  the 
Vitreous  is  occupied  by  the  vitreous  body.  These  are 
large  lymph  spaces,  and  are  connected  with  one  another, 
and  with  the  other  spaces  of  the  eyeball. 

The  circulation  of  the  eyeball  is  carried  on  by  the  CENTRAL 

ARTERY  OF  THE  RETINA,  the  LONG  and  SHORT  POSTERIOR  and 
the  ANTERIOR  CILIARY  ARTERIES. 

The  RETINAL  ARTERY  passes  into  the  eyeball  through  the 
center  of  the  optic  nerve,  and  forms  a  whorl  of  branches 
upon  its  entrance.  These  vessels  extend  to  the  ora  serrata. 
The  layer  of  rods  and  cones  and  the  macula  lutea  possess 
no  blood-vessels.  The  blood  is  collected  by  venous  stems, 
which  form  the  central  vein  of  the  retina  that  has  a  course 
parallel  to  the  artery. 

The  SHORT  POSTERIOR  CILIARY  arteries  are  about  twenty 
19 


2 90  THE   EYEBALL  AND   LACRIMAL   SYSTEM. 

Cornea  ,Sr 


Ora 

Ciliary  Serrata. 

Processes. 


a  Anterior  ciliary  artery. 

d  Anterior  ciliary  vein. 

/?  connection  with  circulus  iridicus  major. 

7  Connection  with  chorio-capillaris. 

d  Arterial  episcleral  branches. 

5'  Venous  episcleral  branches. 

e  Arterial  conjunctival  branches. 

<?  Venous  conjunctival  branches. 

r?  Arterial  branches  to  corneal  junction 

•/I  Venous  branches  to  corneal  junction. 

V  Venae  vorticosae. 

S  Venous  sinus  of  sclera. 


FIG.  95. — VESSELS  OF  THE  EYE.     External  tunic,  stippled;  middle  tunic, 

white;  internal  tunic  and  optic  nerve,  stippled  criss-cross; 

arteries,  light;  veins,  dark. 

Central  vessels  of  retina;  a.  artery;  a1 '.  vein;  ft,  c,  d.  anastomoses  with  vessels 
of  sheath,  short  posterior  ciliary  arteries  and  choroidal  vessels,  respect- 
ively. 

A,  inner,  B,  outer  sheath  vessels;  r.  short  posterior  ciliary  artery;  I',  vein; 
II.  episcleral  artery;  II'.  veins;  III.  capillaries  of  chorio-capillaris. 
i.  long  posterior  ciliary  artery;  2.  circulus  iridicus  major;  3.  branches 
to  ciliary  body;  4.  to  iris  (Stohr's  Histology}. 


THE    CIRCULATION    OF    THE    EYEBALL.  2QI 

in  number.  They  pierce  the  sclera  near  the  entrance  of  the 
optic  nerve,  and  pass  into  the  choroid.  As  they  pass 
through  the  sclera,  they  give  off  branches  that  supply  the 
posterior  half  of  this  coat.  In  the  choroid,  these  vessels 
form  the  chorio-capillaris.  Their  branches  anastomose 
with  branches  of  all  others,  including  those  of  the  central 
artery  of  the  retina. 

The  LONG  POSTERIOR  CILIARY  arteries  pierce  the  sclera 
near  the  optic  nerve,  and  pass  to  the  ciliary  region  between 
the  choroid  and  sclera.  At  the  base  of  the  iris,  they  form 
a  circle  of  vessels,  the  CIRCULUS  ARTERIOSUS  IRIDICUS 
MAJOR,  which  sends  branches  to  the  ciliary  processes,  the 
choroid  and  the  iris;  the  latter  branches  pass  to  the 
pupillary  region,  where  they  form  the  CIRCULUS  IRIDICUS 
MINOR. 

The  ANTERIOR  CILIARY  arteries  are  derived  from  the 
vessels  of  the  recti  muscles.  These  penetrate  the  sclera 
near  the  corneo-scleral  junction.  Their  branches  nourish 
the  anterior  half  of  the  sclera,  the  conjunctiva,  the  ciliary 
muscle,  and  the  anterior  half  of  the  choroid;  they  connect 
with  the  circulus  iridicus  major,  and  form  a  network  of 
capillaries  at  the  corneo-scleral  junction.  Around  the 
optic  nerve,  there  is  some  anastomosis  between  the  branches 
of  the  ciliary  arteries. 

The  blood  is  returned  by  the  VEN^E  VORTICOSE,  which 
are  four  to  six  in  number.  These  run  a  course  entirely 
different  from  that  of  the  arteries.  Each  is  formed  by  a 
whorl  of  veins,  and  passes  through  the  sclera  to  empty  into 
the  ophthalmic  veins.  The  blood  from  the  anterior  ciliary 
arteries  is  carried  by  the  anterior  ciliary' veins  that  run 
parallel  to  the  arteries.  These  also  receive  the  blood  from 
the  episcleral  spaces. 

The  lymphatics  are  extensive,  and  form  a  series  of  inter- 
communicating spaces. 


292  THE    EYEBALL  AND    LACRIMAL    SYSTEM. 

ANTERIORLY,  the  spaces  in  the  cornea  communicate  with 
those  of  the  sclera,  and  with  the  canal  of  Schlemm  and  the 
anterior  chamber,  by  means  of  the  spaces  of  Fontana. 

The  ANTERIOR  CHAMBER  communicates  with  the  posterior 
chamber,  and  through  this,  with  the  canal  of  Petit. 

POSTERIORLY,  the  lymphatics  of  the  optic  nerve  com- 
municate with  the  subarachnoidean  space,  on  the  one  hand, 
and  the  hyaloid  canal  and  perivascular  spaces  of  the  retina, 
on  the  other. 

The  space  of  Tenon  lies  external  to  the  sclera,  and  re- 
ceives lymph  from  the  subscleral  space,  directly,  and  by 
way  of  the  channels  around  the  venae  vorticosae;  the 
lymph  is  sent  to  the  spaces  around  the  optic  nerve.  The 
latter  communicate  with  those  of  the  central  nerve 
system. 

The  nerves,  long  and  short  ciliary,  supply  the  choroid 
and  pass  between  it  and  the  sclera;  at  the  ciliary  body, 
they  form  the  ciliary  ganglion  plexus,  that  supplies  the 
ciliary  muscle,  iris  and  cornea  and  vessels.  Those  of  the 
iris  form  a  circular  plexus.  The  nerves  of  the  cornea  have 
been  considered. 

THE  APPENDAGES  OF  THE  EYEBALL. 

The  Appendages  are  the  Eyelids,  Conjunctiva  and  the 
Caruncle. 

The  Eyelid  consists  of  a  double  fold  of  skin,  the  under 
surface  of  which  has  become  modified  to  form  a  MUCOUS 
MEMBRANE.  This  is  the  CONJUNCTIVA,  which  is  composed 
of  stratified  columnar  cells  that  rest  upon  a  basement  mem- 
brane and  tunica  propria.  Among  the  epithelial  cells  some 
goblet  cells  are  seen.  Over  its  greater  extent,  the  conjunc- 
tiva is  smooth,  but  toward  the  region  opposite  to  the  free 
edge,  folds  are  formed. 


THE    EYELID. 


293 


Beneath  the  tunica  propria  is  found  a  dense  plate  of 
white  fibrous  tissue  called  the  TARSAL  PLATE  (incorrectly 
called  cartilage).  This  is  wedge-shaped,  with  its  thicker 


Hb 


W 


McR 


FIG.  96. — SAGITTAL  SECTION  OF  EYELID  OF  A  CHILD  Six  MONTHS  OLD 
(Stohr's  Histology). 

i.  Skin:  E.  epidermis;  C.  derma;  Sc.  subcutaneous  tissue;  Hb.  lanugo  hairs; 
K.  sweat-glands;  W.  eyelash;  Eh.  developing  lash;  W,  W".  portions  of 
follicle  of  eyelashes;  M.  portion  of  a  ciliary  gland.  2.  Orbicularis 
palpebrarum  muscle;  O.  transverse  section  of  same;  McR.  tarsal  muscle. 

3.  Tendon  of  levator  palpebrarum  superior;  mps.  superior  levator  muscle; 

4.  Conjunctival  portion;  e.  epithelium;  tp.  tunica  propria;  at.  accessory 
tear  gland;  t.  tarsus;  m.  tarsal  gland  (Meibomian);  a.  arcus  tarseus 
externus;  5.  margin  of  eyelid. 


2Q4  THE   EYEBALL  AND   LACRIMAL    SYSTEM. 

edge  at  the  margin  of  the  lid.  It  extends  a  little  over  one- 
half  the  height  of  the  lid,  and  at  its  end,  an  ACCESSORY  TEAR 
gland  is  found,  the  GLAND  OF  KRAI  si:.  Il  contains  a 
number  of  compound  racemose  glands,  the  ducts  of  which 
open  upon  the  free  margin.  These  are  the  MEIBOMIAN,  or 
TARSAL,  GLANDS,  and  number  about  thirty  in  the  upper,  and 
a  few  less  in  the  lower  lid.  They  resemble  sebaceous  glands, 
and  the  ducts  are  lined  by  stratified  squamous  cells.  At 
the  margin  of  the  lid  muscles  fibres  marginal  muscle  are  seen 
behind  the  ducts.  These  glands  secrete  an  oily  substance 
that  lubricates  the  edges  of  the  lids,  prevents  them  from 
uniting,  and  ordinarily  keeps  the  tears  from  overflowing. 

Between  the  tarsal  plate  and  the  upper  skin  surface,  is 
found  the  SUBCUTANEOUS  FIBROUS  TISSUE.  In  this  layer 
is  the  muscle  of  the  eyelid,  which  is  chiefly  of  the  voluntary 
variety,  although  some  smooth  muscle  is  present.  Some 
voluntary  muscle  fibres  are  found  between  the  cilia  and 
Meibomian  gland;  these  constitute  the  musculus  cilians 
Riolani.  In  the  tarsal  connective  tissue  are  found  smooth 
muscle  fibres  that  are  attached  to  the  proximal  end  of  the 
tarsal  plates;  these  constitute  the  LID-MUSCLE  OF  MUELLER. 
Diffuse  lymphoid  tissue  is  seen  in  varying  quantities  in  the 
tunica  propria. 

The  SKIN  covers  the  outer  surface.  Its  structure  is  the 
same  as  in  other  places,  and  it  contains  many  sebaceous  and 
sweat-glands  and  fine  hairs.  Pigmented  cells  are  found  in 
the  corium.  Very  little  fat  is  found  in  the  loose  subcu- 
taneous tissue. 

At  the  edge  of  the  lid,  are  seen  two  rowrs  of  heavy  hairs, 
the  CILIA,  or  EYELASHES.  They  pass  deeply  into  the  corium, 
and  last  about  four  months.  Between  the  cilia  and  the 
ducts  of  the  Meibomian  glands,  are  some  coiled  tubular 
structures  called  the  GLANDS  OF  MOLL.  These  are  CEKT- 
MINOUS  GLANDS,  and  resemble  those  of  the  external  ear. 


THE    CARUNCLE.  295 

Their  ducts  at  times  are  seen  to  open  into  the  follicles  of 
the  cilia. 

The  skin  at  the  conjunctival  margin  forms  an  acute  angle, 
while  above  the  ciliary  region  the  angle  is  obtuse.  This 
serves  to  distinguish  these  two  margins. 

The  Conjunctiva  lines  the  under  surface  of  the  eyelid, 
and  is  then  reflected  over  the  eyeball  from  the  insertion  of 
the  muscles  to  the  cornea.  Here  the  stratified  cells  alone 
continue  upon  this  organ.  It  consists  of  stratified  columnar 
cells,  basement  membrane  and  tunica  propria.  In  the  latter 
lymphoid  tissue  is  often  present  in  abundance. 

At  the  inner  angle,  or  CANTHUS,  of  the  lids  is  seen,  in 
lower  animals,  a  THIRD  EYELID.  This  is  called  the  PLICA 

SEMILUNARIS,    Or    MEMBRANA    NICTITANS.       In   lower   forms, 

a  distinct  tarsal  plate  is  present,  which  is  seldom  present  in 
man.  Here  it  is  usually  a  small  fold,  covered  by  stratified 
squamous  cells,  in  which  some  glands  may  be  found. 

The  Caruncle  is  a  little  patch  of  skin  at  the  inner  canthus. 
It  contains  hair  follicles,  sweat-glands,  adipose  and  mus- 
cle tissues  within  its  corium,  and  is  covered  by  stratified 
squamous  cells.  A  little  voluntary  striated  and  some 
smooth  muscle  tissues  are  present. 

Within  the  eyelid,  two  arterial  arches  are  formed,  one 
at  the  upper  edge  of  the  tarsus,  the  external,  and  the  other 
at  the  edge  of  the  lid,  the  internal.  These  arches  are  pro- 
duced by  the  vessels  coming  from  the  inner  and  outer 
canthi.  The  smaller  branches  pass  to  the  glands  and  con- 
junctiva of  the  lid,  where  they  form  delicate  plexuses. 

The  lymphatics  form  a  close,  delicate  plexus  beneath  the 
conjunctiva,  and  a  loose  set  at  the  upper  margin  of  the  lid, 
that  communicate  with  each  other.  The  branches  of  the 
latter  possess  valves. 

The  nerves  give  off  branches  to  the  muscles  and  skin,  and 
then  form  a  plexus  beneath  the  conjunctiva.  The  latter 


296  THE    EYEBALL  AND    LACRIMAL    SYSTEM. 

supplies  the  glands,  cilia  and  conjunctiva,  forming,  in  the 
latter,  a  subepithelial  plexus  and  sensor  organs,  such  as 

CONJUNCTIVAL  CORPUSCLES  and  BULBS. 

THE  LACRIMAL  APPARATUS. 

The  Lacrimal  Apparatus  consists  of  the  Lacrimal  Gland, 
the  Canaliculi,  the  Lacrimal  Sac  and  the  Nasolacrimal  Duct. 

The  Lacrimal  Gland  is  a  compound  tubular  organ  of  a 
serous  character.  Like  the  mammary  gland,  it  is  a  multiple 
compound  gland,  as  it  is  composed  of  six  or  seven  individual 
glands  merely  bound  into  one  mass.  Each  has  its  own 
duct  that  opens  upon  the  conjunctival  surface. 

Each  Gland  is  covered  by  a  delicate  CAPSULE  of  white 
fibrous  tissue  that  divides  it  into  LOBES  and  LOBULES.  The 
LOBULES  consist  of  the  TUBULAR  ACINI,  which  are  lined  by 
simple  cuboidal  cells.  The  protoplasm  of  these  is  granular, 
and  the  nuclei  have  a  basal  position.  These  cells  rest  upon 
a  basement  membrane,  which  is  supported  by  interstitial 
connective  tissue  of  a  fibre-elastic  nature.  The  ducts  are 
lined  by  simple  columnar  cells. 

The  blood-vessels  are  numerous  and  form  close  capillary 
plexuses  around  the  tubular  acini. 

The  nerves  form  a  subepithelial  plexus,  but  the  exact 
mode  of  ending  is  not  known. 

Each  Canaliculus  has  a  lining  of  stratified  squamous  cells 
that  rest  upon  the  tunica  propria  and  fibre-elastic  layer. 
Outside  of  the  tunica  propria  is  seen  some  voluntary  striated 
muscle,  chiefly  longitudinally  arranged. 

The  opening  of  the  canaliculus  is  called  the  puncta,  and  at 
this  point  some  of  the  muscle  fibres  are  circularly  disposed, 
forming  sphincter  muscles. 

The  Sac  and  Duct  are  lined  by  stratified  columnar  cells. 
In  the  tunica  propria,  considerable  diffuse  lymphoid  tissue 


THE    LACRIMAL   APPARATUS.  297 

is    found.      Occasionally,  in    the   lower   end   of    the   duct, 
ciliated  epithelial  cells  are  present. 

Within  the  orbit,  the  eyeball  is  surrounded  by  a  serous 
membrane  called  the  capsule  of  Tenon.  The  space  en- 
closed is  the  space  of  Tenon,  or  the  episcleral  lymph  space. 
This  space  aids  in  the  movement  of  the  eyeball. 


CHAPTER  XIX. 


THE  EAR. 

The  Ear  is  made  up  of  three  parts,  the  External,  Middle 
and  Internal. 

The  EXTERNAL  EAR  receives  the  sound  waves  and  con- 
ducts them  to  the  MIDDLE  EAR.  The  vibrations  of  the 
DRUM  are  carried  across  the  middle  ear  and  conducted  into 
the  INTERNAL  EAR,  where  they  are  translated  into  the  proper 
nerve  impulses  and  conveyed  to  the  temporal  lobe. 

The  External  Ear  consists  of  the  Pinna  and  a  short 
Canal,  the  External  Auditory  Canal. 

The  Pinna  is  covered  upon  both  sides  by  skin  and  in 
its  center  possesses  a  mass  of  ELASTIC  CARTILAGE.  It  is 
very  irregular,  but  adapted  to  catch  sound  waves.  The 
skin  possesses  hair  follicles  and  sebaceous  glands.  The 
LOBE,  the  lower  soft  portion,  contains  no  cartilage  and  is 
very  vascular. 

The  External  Auditory  Canal  consists  of  OUTER,  CAR- 
TILAGINOUS and  INNER,  BONY  portions.  The  OUTER  part  is 
lined  by  skin,  in  the  corium  of  which  are  found  CERUMINOUS 
GLANDS.  These  are  coiled  tubular  organs  that  form  the 
wax.  Hairs  are  very  abundant  here.  In  the  INNER,  or 
OSSEOUS,  portions,  hairs  and  glands  are  absent,  and  the 
tunica  propria  is  closely  attached  to  the  periosteum  of  the 
bone.  The  uppermost  layers,  at  least,  of  the  epithelium 
that  lines  the  external  auditory  canal  moves  constantly 
from  within,  outward.  By  this  means  the  cerumen  is 
ordinarily  moved  to  the  outlet. 

The  Tympanic  Membrane,  or  Drum,  separates  the 

298 


THE    MIDDLE    EAR.  2 99 

MIDDLE  from  the  EXTERNAL  EAR.  Externally,  it  is  covered 
by  stratified  squamous  cells  continued  from  the  skin.  In 
this  location,  the  stratum  corneum  is  nucleated,  and  the 
corium  is  thin,  except  in  the  region  of  the  handle  of  the 
malleus.  The  middle  portion  consists  of  white  fibrous 
tissues  arranged  as  RADIAL,  or  EXTERNAL,  and  CIRCULAR,  or 
INTERNAL  fibres. 

The  former  becomes  thinner  toward  the  center  of  the 
tympanum  and  disappears  entirely.  The  CIRCULAR  fibres 
are  more  numerous  externally,  and  become  thinner  toward 
the  handle  of  the  malleus,  where  they  disappear.  Between 
these  two  layers  is  a  small  amount  of  loose  connective  tis- 
sue. Peripherally,  the  fibrous  layer  becomes  thickened  to 
form  the  ANNULUS  FIBROSUS.  The  internal  surface  is  cov- 
ered by  simple  squamous,  or  columnar  cells  that  rest  upon 
a  basement  membrane.  In  the  flaccid  area  of  the  drum,  the 
middle  layer  is  absent,  so  that  the  internal  and  external 
layers  touch  each  other. 

The  Middle  Ear,  or  Tympanum,  is  an  irregular  cavity 
within  the  bone  and  is  connected  with  the  pharynx  by  the 
Eustachian  Tube.  This  maintains  an  equal  pressure  upon 
both  sides  of  the  membrane.  The  mucous  membrane 
lining  these  portions  is  covered  by  pseudo- stratified  ciliated 
epithelium.  The  cilia  are  absent  upon  the  EAR  BONES, 
LIGAMENTS  and  MEMBRANA  TYMPANi.  Small  mucous  glands 
are  found  in  the  tunica  propria.  The  ANTRUM  and  MASTOID 
CELLS  are  lined  with  low  polygonal  cells. 

The  Ear  Bones  are  the  MALLEUS,  INCUS  and  STAPES. 
These  are  small  masses  of  osseous  tissue,  by  means  of  which 
the  sound  waves  are  transmitted  from  the  drum  to  the  in- 
ternal ear.  In  the  thickest  portions  they  possess  Haver- 
sian  systems.  Their  articular  surfaces  are  covered  with 
hyalin  cartilage.  The  stapes  alone  possesses  a  marrow 
cavity. 


300  THE   EAR. 

The  MEMBRANE  closing  the  FENESTKA  ROTUNDA  that 
leads  to  the  internal  ear  consists  of  connective  tissue. 
Its  middle  ear  surface  is  covered  by  nonciliated  cells,  while 
that  which  lies  in  the  internal  ear  is  covered  by  endothelial  cells. 

The  OSSEOUS  portion  of  the  EUSTACHIAN  TUBE  is  lined  by 
a  thin  mucous  membrane  that  is  closely  adherent  to  the 
periosteum.  The  lining  cells  are  pseudo- stratified  ciliated 
elements.  Glands  are  absent.  In  the  CARTILAGINOUS  por- 
tion, the  mucosa  is  thicker,  and  is  lined  by  stratified  ciliated 
cells,  among  which  there  are  a  large  number  of  goblet  cells. 
In  the  tunica  propria,  mucous  glands  and  diffuse  lymphoid 
tissue  are  seen,  and  the  latter  may  be  formed  into  solitary 
follicles  near  the  pharyngeal  end. 

The  blood  supply  to  the  tympanic  membrane  is  impor- 
tant. Its  external  surface  is  supplied  by  capillaries  derived 
from  the  vessels  of  the  external  canal,  while  the  inner  sur- 
face receives  vessels  from  those  of  the  middle  ear.  The 
mucosa  of  the  Eustachian  tube  receives  blood  from  both  the 
middle  ear  and  pharyngeal  vessels. 

Lymphatic  vessels  follow  those  of  the  circulatory  system. 
Those  of  the  external  surface  of  the  membrana  tympani 
empty  into  those  of  the  external  canal,  while  those  of  the 
inner  surface  empty  into  those  of  the  tympanum.  The 
latter  lie  in  the  deeper  portions  of  the  tunica  propria,  and 
at  intervals  possess  dilatations. 

The  nerves  of  the  external  surface  of  the  tympanic  mem- 
brane are  derived  from  the  auriculo temporal;  in  addition 
to  these,  fibres  enter  at  the  edge.  Both  form  a  close 
plexus.  This  supplies  the  external  surface  by  a  subepithe- 
lial  plexus.  The  inner  surface  is  supplied  by  the  tympanic 
plexus,  which  sends  branches  to  the  epithelial  layer. 
Occasionally,  minute  ganglia  are  present.  The  Eustachian 
tube  receives  fibres  from  the  tympanic,  as  well  as  from  the 
pharyngeal  plexuses. 


THE    INTERNAL    EAR.  301 

THE  INTERNAL  EAR. 

The  Internal  Ear,  or  Labyrinth,  consists  of  Sacculus, 
Utriculus,  Semicircular  Canals  and  Cochlea. 

The  Labyrinth  consists  of  the  OSSEOUS  and  MEMBRANOUS 
portions,  which  are  separated  from  each  other  by  a  lymph 
space.  The  BONY  LABYRINTH  surrounds  the  MEMBRANOUS 
portion,  and  is  separated  from  it  by  the  PERILYMPH. 
Within  the  membranous  part  is  the  ENDOLYMPH. 

SACCULUS  AND  UTRICULUS. 

The  Sacculus  and  Utriculus  are  two  cavities  of  unequal 
size,  which  do  not  communicate  with  each  other  directly, 
but  with  the  DUCTUS  ENDOLYMPHATICUS  by  two  small  canals. 
The  Sacculus  is  the  smaller,  and  lies  anterior  to  the  utricu- 
lus.  The  Utriculus  is  connected  with  the  semi-circular 
canals,  while  the  sacculus  communicates  with  the  cochlear 
portion  of  the  membranous  labyrinth  by  means  of  the 

DUCTUS  REUNIENS. 

The  bony  walls  are  covered  by  periosteum,  which  is 
lined  by  a  layer  of  endothelial  cells  continued  over  the 
trabeculae,  that  extend  from  the  periosteum  to  the  mem- 
branous labyrinth.  From  this  point  the  endothelium  con- 
tinues over  the  external  surface. 

The  walls  of  the  membranous  saccule  and  utricle  are  com- 
posed of  bundles  of  white  fibrous  tissue  arranged  into  two 
layers  of  variable  thickness,  5  to  15  microns.  The  thickest 
portions  are  where  the  nerve  fibres  leave  the  maculae 
acusticae  and  maculae  cribrosae.  The  cells  lining  these 
vesicles  consist  of  simple  polygonal  epithelium,  3  to  4  microns 
in  height,  except  over  the  MACULA  ACUSTIC^,  where  they 
are  of  the  NEURO-EPITHELIAL  variety.  Upon  approaching 
these  areas,  the-  polygonal  change  to  cuboidal  and  become 
progressively  higher  until  a  height  of  30  microns  is  reached. 


302  THE   EAR. 

These  cells  are  of  two  varieties,  SUSTENTACULAR,  or  SUP- 
PORTIVE,  and   SPECIAL,   NEURO-EPITHELIAL,   Or  HAIR-CELLS. 

The  SUSTENTACULAR  cells  are  very  long,  irregular  col- 
umns, the  basal  portions  of  which  are  branched.  The 
large  nuclei,  located  at  various  levels  in  the  inner  half  of  the 
cell,  produce  a  bulging  of  the  cell-body.  The  granular 
protoplasm  possesses  PIGMENT  GRANULES  of  a  yellowish 
color. 

The  SPECIAL,  or  HAIR-CELLS,  are  also  columnar,  but  not  as 
long  as  the  preceding,  and  extend  through  only  one-half  of 
that  layer.  The  basal  portion  of  these  cells  is  broad,  and 
contains  large  round  nucleus.  The  distal  end  is  rounded 
and  possesses  a  cuticular  border,  the  CUPOLA,  from  which 
projects  a  CONICAL  CILIUM  20  microns  long.  This  extends 
into  the  endolymph.  Closer  examination  shows  that  the 
cilium  consists  of  many  finer  hairs.  The  protoplasm  of 
these  cells  is  granular  and  contains  a  yellowish  pigment. 

The  Otoliths  are  small,  prismatic  calcium  carbonate 
crystals,  i  to  15  microns  long,  occurring  in  the  vesicles,  and 
imbedded  in  a  gelatinous  substance,  the  Otolith  membrane, 
that  covers  the  neuro-epithelial  cells.  This  otolith  mem- 
brane contains  many  of  these  prisms. 

The  Ductus  Endolymphaticus  and  its  dilated  extremity, 
the  Sacculus,  have  the  same  structure  as  saccule  and 
utricle. 

A  plexus  of  nerve  fibres  is  found  beneath  the  neuro-epi- 
thelium.  The  fibres  extend  into  the  epithelial  layer,  and  as 
they  pierce  the  basement  membrane,  the  myelin  sheath 
blends  therewith,  and  leaves  the  dendrite  free.  These 
latter  form  fibrillae  that  are  connected  with  the  neuro- 
epithelial  (hair)  cells;  some  pass  higher  between  the  sup- 
portive cells. 

In  these  areas,  the  capillary  plexuses  are  especially 
numerous. 


THE    SEMICIRCULAR    CANALS.  303 

THE  SEMICIRCULAR  CANALS. 

The  Membranous  Semicircular  Canals  are  united  to  the 
periosteum  by  TRABECUL^,  as  in  the  preceding,  and  the 
endothelial  cells  pursue  the  same  course  in  the  lymph 
space.  The  epithelium  resembles  that  of  the  saccule  and 
utricle,  being  polygonal,  but  slightly  larger,  varying  from 
12  to  1 6  microns.  Specialized  areas,  GRISTS  ACUSTIC^, 
are  found  in  the  floor  of  the  AMPULLA  (dilated  portions  at 
the  junctions  of  the  canals).  Here  the  thickened  fibrous 
wall  forms  the  TRANSVERSE  SEPTUM.  The  specialized  areas 
resemble  those  of  the  saccule  and  utricle.  The  hairs  of  the 
neuro-epithelial  cells  are  unusually  long,  some  reaching  to 
the  middle  of  the  lumen.  They  are  called  the  AUDITORY 
HAIRS,  and  arise  from  the  CUPOLA  of  the  cells. 

The  nerve  fibres  pass  to  the  thick  TRANSVERSE  SEPTUM, 
and  form  a  plexus  from  which  finer  fibres  follow  the  same 
course  as  in  the  saccule  and  utricle. 

The  blood-vessels  are  distributed  in   the  same  manner. 

THE  COCHLEA. 

The  Cochlea  consists  of  a  SPIRAL  BONY  CANAL  that  winds 
around  the  central,  vertical  AXIS,  or  MODIOLIS.  The  bony 
canal  is  separated  into  an  UPPER,  the  SCALA  VESTIBULI,  and 
a  LOWER,  the  SCALA  TYMPANI.  These  divisions  are  further 
separated  by  a  central  shelf  of  bone  called  the  LAMINA 
SPIRALIS.  This  extends  about  half  of  the  way  across,  and 
the  BASILAR  MEMBRANE  completes  the  partition.  At  the 
upper  end  of  the  cochlea,  these  canals  communicate  with 
each  other;  both  contain  the  PERILYMPH. 

The  Ductus  Cochlearis,  or  Scala  Media,  is  a  delicate, 
triangular,  membranous  canal  that  lies  in  the  scala  ves- 
tibuli;  its  outer  basal  angle  is  attached,  externally,  to  the 
outer  wall,  and  the  inner  angle,  internally,  to  the  lamina 


3°4 


THK    EAR. 


spiralis.  It  contains  the  endolymph,  and  has  an  important 
epithelial  lining.  The  BASILAR  MEMBRANE  separates  it 
from  the  SCALA  TYMPANI,  and  the  MEMBRANE  OF  REISSNER 
from  the  SCALA  VESTIBULI.  The  latter  membrane  is  quite 
thin,  about  3  microns,  and  extends  from  the  lamina  spiralis 
(internal  to  the  crista)  to  the  bony  wall  of  the  scala  vestibuli 
at  an  angle  of  about  45  degrees.  Upon  its  VESTIBULAR 


FIG.  97. — HORIZONTAL  SECTION  THROUGH  PETROUS  BONE  OF  A  KITTEN 
(Stohr's  Histology}. 

i.  Ganglion  spirale;  2.  macula;  3.  ganglion  vestibulare;  4.  meatus  acusticus 
internus;  5.  vestibular,  and  6.  cochlear  divisions,  respectively,  of  the 
acoustic  nerve;  7.  scala  tympani;  8.  scala  vestibuli;  9.  bone;  10.  modiolus. 
x.  scala  media. 

WALL,  it  is  covered  by  a  layer  of  pigmented  endothelial  cells 
which  rest  upon  the  middle  connective  tissue  layer,  in 
which  capillaries  are  found.  The  epithelial  lining  of  its 
inner  surface  consists  of  a  single  layer  of  polygonal  cells. 
The  OUTER  WALL  of  the  scala  media,  for  about  two-thirds 
of  its  distance  from  the  upper  angle,  is  covered  by  cuboidal 
cells,  within  which  there  are  quite  a  number  of  capillaries, 


THE    COCHLEA. 


305 


a  very  unusual  condition.  This  is  the  STRIA  VASCULARIS. 
At  the  lower  margin  of  the  latter  is  a  small  projection,  the 
PROMINENTIA  SPIRALS;  this,  with  the  lower  part  of  the  outer 
wall,  is  covered  by  flattened  cells  that  become  columnar 
as  the  basilar  membrane  is  reached.  The  tissue  external 


FIG.  98. — SCHEME  OF  THE  STRUCTURE  OF  THE  TYMPANIC  WALL  OF  THE  DUCT 

OF  THE  COCHLEA  (Stohr's  Histology). 
A.  Side  view;  B.  surface  view.  a.  auditory  teeth;  b.  epithelium  of  sulcus 

spiralis;  c.  inner  hair  cells;  d.  inner  head  plates;  e.  outer  head  plates;/. 

phalanges;  g.  outer  hair  cells;  h.  cells  of  Hensen;  i.  cells  of  Claudius. 

i.  Nerve;  2.  first  spiral  cord;  3.  inner  pillar  cells;  4.  vasspirale;  5.  tunnel; 

6.  outer  pillar  cells;   7.  Nuel's  spaces;  8.  Deiter's  cells;  9.  membrana 

basilaris;  10.  tympanal  lamelli. 

to  these  cells  is  quite  thick,  and  extends  over  the  vestibular 
wall  above  the  attachment  of  Reissner's  membrane,  and 
below  the  attachment  of  the  basilar  membrane.  This  is 
the  LIGAMENTUM  SPIRALS.  At  the  attachment  of  the 
basilar  membrane  this  ligament  forms  a  projection  called 

the  CRISTA  BASILARIS. 


306  THE   EAR. 

The  FLOOR  of  the  ductus  cochlearis  (tympanic  side)  con- 
sists of  the  BASILAR  MEMBRANE  that  unites  the  SPIRAL 
PROMINENCE  to  the  spiral  lamina;  this  is  completed  by  the 
LIMBUS  that  extends  from  the  end  of  the  spiral  lamina  to  the 
attachment  of  Reissner's  membrane. 

The  outer  portion  of  the  LIMBUS  is  thicker  near  the  mem- 
brane, due  to  an  increase  in  the  periosteum.  This  portion 
contains  clefts  and  depressions  that  deepen  toward  the  inner 
half,  at  which  point  the  cleft  is  quite  deep,  and  little 
projections,  separated  by  lateral  clefts,  give  rise  to  the 
AUDITORY  TEETH,  which  number  about  2,500.  These 
TEETH  and  projecting  areas  are  covered  by  simple  polyg- 
onal cells,  while  the  CLEFTS  are  lined  by  columnar  elements. 
The  inner  half  of  the  LIMBUS  consists  of  a  slightly  projecting 
mass,  the  SUPERIOR  LIP,  due  to  the  sudden  decrease  in 
thickness,  and  a  lower  portion  that  continues  over  the  bony 
lamina  toward  the  basilar  membrane;  the  LATTER  is  the 
INFERIOR  LIP.  Between  these  lies  a  little  space,  the 
SULCUS  SPIRALIS,  due  to  the  sudden  decrease  in  thickness  of 
the  periosteum.  The  SULCUS  is  lined  by  flat  cells. 

The  BASILAR  MEMBRANE  is  covered  on  its  tympanic  sur- 
face by  the,.TYMPANic  LAMELLA,  made  up  of  spindle-shaped 
cells  and  delicate  fibres,  representing  an  incomplete  change 
to  endothelial  cells.  This  is  continuous  with  the  periosteum 
of  the  scala  tympani.  Above  this  layer  is  the  membrana 
propriay  that  represents  a  greatly  hyper trophied  basement 
membrane  and  seems  to  support  the  epithelium  upon  its 
upper  surface.  The  outer  end  of  the  basilar  membrane  is 
covered  by  the  CELLS  OF  CLAUDIUS  that  continue  toward  the 
outer  wall  and  pass  into  columnar  and  flattened  elements 
that  are  found  upon  the  basilar  crest.  These  cells  possess 
spherical  nuclei  imbedded  in  a  slightly  granular  and  pig- 
men  ted  protoplasm;  they  represent  a  continuation  of  the 
CELLS  OF  HENSEN.  Between  the  limbus  and  the  cells  of 


THE    ORGAN    OF    CORTI.  307 

Claudius  lies  the  ORGAN  OF  CORTI;  composed  of  NEURO- 
EPITHELIAL  and  SUSTENTACULAR  CELLS.  This  organ  is 
divided  into  an  inner  portion,  the  MEMBRANATECTORIA,  and 
an  outer  part,  the  ZONA  PECTINATA. 

The  CELLS  of  the  Organ  of  Corti  are  the  PILLAR,  HAIR  and 

SUSTENTACULAR  CELLS. 

The  PILLAR  CELLS  are  peculiar  S-shaped  elements  pos- 
sessing a  striated  body,  surrounded  by  a  narrow  band  of 
protoplasm.  The  latter  is  thickene^.  at  the  base  (tunnel 
side),  and  in  this  part  is  seen  the  nucleus.  The  lower  end 
rests  upon  the  basilar  membrane,  and  is  expanded  to  form 
the  FOOT;  the  upper  end  likewise  undergoes  an  expansion, 
termed  the  HEAD.  These  cells  form  two  rows,  inner  and 
outer;  they  articulate  above,  and  form  a  triangular  canal 
called  CORTI'S  TUNNEL.  This  contains  a  semi-solid  inter- 
cellular substance.  The  inner  cell,  being  shorter,  is  more 
nearly  vertical,  and  its  head  bears  an  articular  facet  for  the 
reception  of  the  articular  head  of  the  outer  cell.  The  inner 
cells  are  more  numerous  and  thinner  than  the  outer,  about 
6,000  to  4,500,  respectively.  The  head  process  of  both 
cells  continues  externally  as  a  thin,  shelf-like  process  called 
the  HEAD-PLATE.  Of  these,  the  INNER  HEAD-PLATES  lie  above, 
but  are  shorter  than  the  OUTER.  The  outer  are  called  the 
PHALANGEAL  PROCESSES,  and  by  their  union  with  the  CELLS 
OF  DEITER,  form  the  MEMBRANA  RETICULARIS. 

The  NEURO-EPITHELIAL  CELLS  are  distributed  upon  the 
inner  and  outer  surfaces  of  the  pillar  cells.  They  are  the 
HAIR  CELLS,  and  of  these  there  are  two  rows,  INNER  and 
OUTER.  Like  the  hair  cells  of  the  preceding,  and  the  neuro- 
epithelial  cells  of  the  nasal  mucous  membrane,  they  are 
about  half  the  length  of  the  sustentacular,  or  pillar  cells, 
and  are  columnar  elements  containing  a  granular  protoplasm 
and  an  oval  nucleus.  The  outer  end  has  a  cuticular  border, 
from  which  about  twenty  hairs  extend.  The  OUTER  CELLS 


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THE    ORGAN    OF    CORTI.  309 

are  longer  and  narrower  than  the  INNER,  and  more  numer- 
ous. Usually  one  hair  cell  is  present  for  each  two  pillar 
cells.  The  outer  hair  cells  are  found  in  three  or  four  rows, 
which  are  separated  by  the  ends  or  phalanges  of  Deiter's 
cells  and  the  membrana  reticularis.  The  inner  row  rests 
upon  the  outer  pillar  cells;  the  cells  of  the  next  row  lie 
opposite  to  the  rods,  and  the  third  row  alternates,  produc- 
ing a  peculiar  checker-board  appearance,  the  ends  of  the  hair 
cells  being  separated  from  one  another  by  the  ends  of  the 
Deiter  cells. 

The  SUSTENTACULAR,  or  DEITER  CELLS  are  INTERNAL  and 
EXTERNAL.  Each  cell  consists  of  a  thin  PYRAMIDAL  PROC- 
ESS and  a  large  BASAL  part  that  contains  the  nucleus. 
The  INTERCELLULAR  SPACES  OF  NUEL,  between  the  cells  of 
the  organ  of  Corti,  contain  a  substance  like  that  in  the 
tunnel  of  Corti.  Internally,  DEITER'S  cells  pass  through 
the  entire  layer,  and  are  continuous  with  the  cells  of  the 
sulcus.  Externally,  they  form  the  phalanges  that  help 
produce  the  membrana  reticularis.  A  surface  view  will 
show  both  sustentacular  and  neuro-epithelium;  a  basal 
view,  however,  will  show  only  sustentacular  elements. 
Just  external  to  the  Deiter  cells  are  other  sustentacular 
elements,  the  CELLS  OF  HENSEN.  These  extend  to  and 
continue  with  those  of  Claudius.  Extending  over  the 
organ  of  Corti  and  arising  from  the  upper  lip  of  the  limbus 
is  a  membrane  composed  of  delicate  fibres  and  interfibrillar 
substance.  This  is  the  MEMBRANA  TECTORIA,  or  CORTI'S 
MEMBRANE.  At  one  time  this  was  part  of  the  cells  beneath, 
those  of  the  sulcus  and  auditory  teeth;  it  represents  a 
cuticular  border. 

The  divisions  of  the  auditory  nerve  are  vestibular  and 
cochlear.  The  vestibular  arises  from  the  sacculus,  utriculus, 
macula  and  the  semicircular  canals  (crisis).  The  cochlear 
portion  arises  in  the  cochlea,  and  is  made  up  as  follows: 


310  THE    EAR. 

In  a  little  bony  canal  in  the  lamina  spirale  is  a  strip  of 
gray  substance  that  is  called  the  GANGLION  SPIRALE.  This 
consists  of  bipolar  cells,  one  branch,  the  dendrite  of  which 
passes  outward  into  the  organ  of  Corti,  while  the  other,  the 
axis  cylinder,  passes  through  a  minute  canal  in  the  axis  to 
the  central  canal,  where  it  meets  other  fibres  from  different 
levels.  These  pass  to  the  base  and  to  the  internal  auditory 
meatus,  as  the  COCHLEAR  BRANCH,  and  then  to  the  oblongata. 
The  dendritic  branches  of  these  ganglion  cells  form  a  plexus 
in  the  minute  canal  of  the  spiral  shelf.  Toward  the  organ 
of  Corti  the  lamina  is  pierced  by  many  canals  called  the 
FORAMINA  NERVOSA  through  which  numerous  fibres,  the 
myelinated  dendritic  branches,  pass,  along  its  inner  epithe- 
lium, to  the  organ  of  Corti.  Upon  entering  these  canals, 
the  myelin  sheaths  and  neurilemmae  are  lost,  and  the 
naked  dendrites,  in  bundles,  continue.  Each  bundle 
separates  into  two,  one  of  which  remains  at  the  inner  sur- 
face and  the  other  passes  along  the  outer  side  of  the  pillar 
cells.  The  latter  lies  in  the  tunnel.  Other  dendrites  cross 
the  tunnel  and  pass  to  the  outer  side  of  the  outer  pillar  cells 
and  form  several  bundles  between  the  Deiter  cells.  From 
these  various  bundles,  fibrillse  connect  with  the  hair  cells. 

The  blood-vessels  follow  the  nerves,  those  of  the  utriculus 
and  sacculus  follow  the  vestibular  branch  and  those  of  the 
cochlea  the  cochlear  division.  After  giving  off  branches  to 
the  first  turn,  the  main  trunk  enters  the  canal  of  the  axis, 
from  which  the  branches  form  the  peculiar  GLOMERULI 
COCHLEA.  Branches  of  the  latter  penetrate  the  scala 
vestibuli,  and  supply,  the  limbus  and  neighboring  tissues. 
Other  branches  continue  over  the  vestibule  to  the  ligamen- 
tum  spirale,  the  stria  vasculare,  and  basillar  membrane  sur- 
rounding the  scala  vestibuli.  The  veins  surround  the  scala 
tympani  and  form  a  trunk  below  the  spiral  ganglion. 


CHAPTER  XX. 


THE  SENSES  OF  SMELL,  TASTE,  AND 
TOUCH. 

THE  ORGAN  OF  SMELL. 

The  Nasal  Mucosa  is  divided  into  RESPIRATORY  and  OL- 
FACTORY portions.  The  lower  portion  of  the  RESPIRATORY 
area,  called  the  VESTIBULE,  is  lined  by  stratified  squamous 
cells  to  the  inferior  turbinate  bone.  Here  a  great  many 
hairs,  sebaceous  and  mucous  glands  that  extend  for  a  short 
distance,  are  encountered.  Above  the  turbinate,  the  epithe- 
lium is  of  the  stratified  ciliated  variety,  and  many  goblet 
cells  are  present.  The  tunica  propria  contains  much  lym- 
phoid  tissue  and  a  large  venous  plexus.  Mucous  and  serous 
glands  are  also  present  in  great  numbers  in  the  region  of  the 
inferior  turbinate  and  nasal  septum.  The  mucosa  is  4  mm, 
thick  in  this  area. 

The  OLFACTORY  MUCOSA  is  usually  prominent  on  account 
of  its  yellow  color,  but  this  does  not  indicate  the  entire 
olfactory  membrane.  It  is  very  thick,  and  ciliated  cells  no 
longer  exist.  The  epithelium  is  of  three  varieties,  the 

SUSTENTACULAR,  NEURO-EPITHELIAL    ELEMENTS   and    BASAL 

cells. 

The  SUSTENTACULAR  cells  are  irregular,  and  possess  an 
OUTER  SEGMENT,  peripheral,  which  is  cylindrical,  and  an 
INNER,  basal,  that  is  narrow  and  irregular.  The  OUTER 
SEGMENTS  form  a  row  of  columnar  elements.  The  oval 
nuclei  form  a  regular  band  or  row\  The  protoplasm  con- 
tains granules  and  pigment  near  the  inner  end,  the  former 


3I2 


THE    SENSE    OF    SMI,!. I.. 


being  arranged  in  rows.  A  cuticular  border  is  present,  and 
forms  the  MEMBRANA  LIMITANS  OLFACTORIA.  The  inner 
segments  are  irregular,  and  usually  branch  at  their  internal 
ends. 

The  NEURO-EPITHELIAL  ELEMENTS  consist  of  peculiar, 
inconspicuous  strips  of  protoplasm  possessing  an  enlarge- 
ment near  the  middle,  in  which  lies  a  large,  round  nucleus. 
The  latter  form  a  band  or  zone  of  spherical  elements.  The 
outer  ends  of  the  rods  extend  to  the  free  surface,  between 
the  supportive  cells,  while  the  inner  ends  pass  to  the  base- 
ment membrane. 


FIG.  ioo. — DIAGRAM  OF  OLFACTORY  MUCOSA. 

a.  Sustentacular  cells;  b.  neuro-epithelial  elements;  c.  basal  cells;  d.  basement 

membrane. 

The  BASAL  cells  are  small  and  irregular  elements  that  send 
processes  between  the  upper  layers  and,  internally,  rest 
upon  the  basement  membrane. 

•The  tunica  propria  consists  of  a  loose  network  of  fibro- 
elastic  tissue.  This  supports  the  mucous  (BOWMAN'S) 
glands,  whose  functionating  epithelium  possesses  a  brown- 
ish pigment.  These  glands  are  numerous,  forming  a  con- 
tinuous layer. 

The  Accessory  Cavities  possess  a  lining  of  ciliated  cells. 
The  mucosa  is  very  thin,  .02  mm.,  and  it  is  firmly  attached 
to  the  periosteum.  Glands  are  very  few  in  the  mucosa  of 
these  cavities. 


THE    ACCESSORY    CAVITIES. 


The  blood-vessels  are  numerous.  The  arterial  branches 
form  a  dense  subepithelial  plexus,  including  a  network 
around  the  glands.  The  veins  are  large  in  number  and  size, 
especially  upon  the  inferior  turbinate. 

The  lymphatics  lie  in  the  lower  part  of  the  tunica  propria; 
in  the  olfactory  area,  an  extra  set  of  vessels  occurs  in  the 
superficial  portion.  These  communicate  with  the  channels 
around  the  nerves. 


FIG.  1 01. — ISOLATED  ELEMENTS  OF  THE  OLFACTORY  MUCOSA. 
a.  Neuro-epithelial  cell;  b.  sustentacular  cells  showing  cuticular  border. 


The  nerves  are  those  of  ordinary  and  special  sensation. 
The  former  are  derived  from  the  trigeminus  and  do  not 
connect  with  the  cells.  The  latter  form  the  olfactory 
nerves.  The  fibres  of  the  olfactory  nerves  arise  from  the 
neuro-epithelial  elements  in  the  form  of  delicate  fibrillae; 
the  latter  join  together,  beneath  the  epithelial  layer,  to 
form  small  bundles  that  are  surrounded  by  perineural 
lymphatic  sheaths;  from  this  position  in  the  tunica  propria 
they  pass  through  the  openings  in  the  cribriform  plate 
of  the  ethmoid  bone  and  terminate  around  the  glomerular 
cells  of  the  olfactory  lobe.  These  fibres  possess  neither 
myelin  sheaths  nor  neurilemmae. 


314  THE    SENSE    OF    TASTE. 

THE  SENSE  OF  TASTE. 

The  Sense  of  Taste  is  due  to  the  Taste-buds.  These  arc- 
not  restricted  to  the  circumvallate  papilla  of  the  tongue, 
but  are  found  in  the  papilla  foliata,  in  the  ventral  surface  of 
the  epiglottis,  at  times  in  the  fungiform  papilla  and  in  the 
soft  palate  and  uvula. 

The  organs  are  barrel-shaped,  and  consist  of  two  varieties 
of  cells,  the  SUSTENTACULAR  and  the  NEURO-EPITHELIAL. 

The  SUSTENTACULAR  CELLS  are  the  OUTER,  and  are  com- 
posed of  a  cell-body  and  a  pointed  end.  The  latter,  with  its 

c  - 

b 


FIG.  102. — TASTE-BUD  FROM  A  PAPILLA   FOLIATA  OF  A  RABBIT. 
i.  Epithelium;  2.  tunica  propria;  a.  taste-bud;  b.  gustatory  hairs;  c.  gustatory 

pore. 

neighbors,  forms  an  opening  at  the  exposed  end  of  the  organ 
called  the  GUSTATORY  PORE.  The  cell-body  varies  in  its 
thickness  and  the  enlargement  may  be  central  or  proximal. 
In  this  enlargement  is  seen  the  large  nucleus. 

The  NEURO-EPITHELIAL  elements  are  peculiar,  long, 
spindle-shaped  cells  possessing  a  nuclear  enlargement. 
This  is  more  pronounced  than  that  of  the  preceding.  The 
peripheral  end  of  each  cell  is  continued  as  a  hair-like  pro- 
jection through  the  gustatory  pore;  this  projection  is  the 

GUSTATORY  HAIR. 

The  nerve  fibres  of  the  nerves  of  taste  arise  between  or 
upon  the  neuro-epithelial  elements  and  represent  the 
dendrites  of  cells  in  the  ganglia  of  the  glossopharyngeal 


THE    SENSE    OF    TOUCH.  315 

nerve  and  the  geniculate  ganglion  that  lies  in  relation  with 
the  facial  nerve.  These  dendrites  pass  into  the  subepi- 
thelial  tissue  and  unite  to  form  bundles  of  fibres  that 
become  myelinated  and  join  the  glossopharyngeal  and 
chorda  tympani  nerves.  Other  sensor  beginnings  lie  in 
the  epithelium  around  the  taste-buds. 

THE  SENSE  OF  TOUCH. 

The  Sense  of  Touch  is  not  limited  to  any  special  region, 
but  it  is  best  developed  in  certain  areas,  as  the  PALM  and 
SOLE.  It  is  restricted  to  the  skin,  and  represents  a  modifi- 


FIG.  103. — CORPUSCLE  OF  MEISSNER  FROM  GREAT  TOE  OF  MAN. 

n.  Myelinated  nerve  fibre;  h.  connective-tissue  sheath;  e.  varicosities.     The 

nuclei  are  invisible  (Stohr's  Histology}. 

cation  of  general  sensibility.     In   the  papillae  of   the  skin, 
especially  that  of  the  sole  and  palm,  are  found  the  TACTILE 

CORPUSCLES  OF  MEISSNER. 

These  are  elongated  structures,  about  50  by  150  microns, 
and  possess  transverse  striations  that  seem  due  to  cells  with 
transversely  placed  nuclei.  These  are  encapsulated  by 
white  fibrous  tissue,  and  are  pierced  at  the  lower  end  by 
nerve  fibres  whose  myelin  sheaths  blend  with  the  capsule. 
The  dendrites  arise  from  telodendria  between  the  cells 


3i6 


THE    SENS!-:    OF    TOITH. 


and  possess  enlargements  at  intervals.  They  pass  to  the 
bottom  of  the  organ,  and  as  they  leave  they  become  myelin- 
ated  and  covered  by  a  neurilemma.  These  myelinated  den- 
drites  pass  to  the  ganglia  of  the  spinal  and  cranial  nerves. 

The  corpuscles  of  Vater,  or  Pacinian  bodies,  are  very 
large,  oval  structures.  Each  consists  of  a  CAPSULE,  an 
INNER  BULB  and  a  KNOB. 

The  CAPSULE  consists  of  many  layers  of  white  fibrous  tis- 
sue, each  separated  from  its  neighbor  by  a  lymph  space 


FIG.  104. — PACINIAN  BODY  FROM  MESENTERY  OF  A  CAT. 

i.  Fat  cells;  2.  artery;  3.  nerve  fibre;  4.  inner  bulb;  5.  dendrite;  6.  layers  of  the 

capsule  (Stohr's  Histology). 

lined  by  endothelial  cells.  These  lamellae  are  held  to- 
gether by  an  INTRA-CAPSULAR  LIGAMENT  that  pierces  all. 
The  INNER  BULB  is  a  cylindric  mass  of  almost  homogeneous 
protoplasm  possessing  nuclei  and  a  slight  enlargement 
called  the  KNOB.  The  knob  represents  the  point  of  origin 
of  the  dendrite  that  leaves  this  organ  as  a  nerve  fibre  as 
in  the  preceding  organ. 


THE  SENSE  OF  TOUCH.  317 

The   CONJUNCTIVAL   CORPUSCLES,   Or   CORPUSCLE   OF 

KRAUSE,  are  also  tactile  corpuscles.  These  are  surrounded 
by  a  delicate  fibrous  CAPSULE,  which  is  surrounded  and 
lined  by  endothelium.  The  center  of  the  corpuscle  seems 
occupied  by  the  divisions  of  the  dendrite  that  arises  here, 
and  by  lymph.  Such  corpuscles  are  found  in  the  con- 
junctiva, edges  of  the  eyelids,  in  the  lips  and  epiglottis. 

The  GENITAL  CORPUSCLES  are  more  complex  than  the 
preceding.  They  may  resemble  the  Pacinian  body,  or  may 
be  composed  of  several  simple  corpuscles  fused  into  one. 
They  are  found  in  the  glans  penis  and  glans  clitoris. 


CHAPTER  XXI. 


DEVELOPMENT  OF  FACE  AND  TEETH. 

The  development  of  the  face  is  a  complicated  process, 
a  number  of  different  fetal  structures  taking  part  therein. 
At  about  the  twelfth  day  of  intrauterine  life  there  appears 
a  depression  upon  the  ventral  surface  of  the  blunt  head- 
process  called  the  ORAL  DEPRESSION,  or  STOMODEUM. 
The  floor  of  this  depression  sinks  deeper,  forming  the 
pharyngeal  membrane,  and  the  margins  become  more 
pronounced.  At  about  the  fifteenth  day  the  lower  boun- 
dary of  the  depression  becomes  formed  upon  each  side  into 
a  finger-like  process,  called  the  FIRST  VISCERAL  ARCH,  that 
soon  divides  into  a  shorter  upper  portion,  the  MAXILLARY 
DIVISION,  and  a  lower  part,  the  MANDIBULAR  DIVISION.  The 
upper  division  forms  now  the  lateral  boundary  and  the  lower 
the  inferior  boundary  of  the  oral  depression.  At  about  the 
same  time  the  tissues  in  the  frontal  region  become  pro- 
jected in  the  form  of  a  blunt  mass  between  the  maxillary 
divisions  of  the  first  arch,  constituting  the  NASO-FRONTAL 
PROCESS.  Thus  the  stomodeum  has  become  a  pentagonal 
fossa.  At  about  the  eighteenth  day  a  second  finger-like 
process  makes  its  appearance  beneath  the  mandibular  por- 
tion of  the  first  arch;  this  is  followed  by  a  third  arch  about 
the  twenty-first  day,  a  fourth  by  about  the  twenty-fourth 
day,  and  the  fifth  and  last  arch  is  formed  by  the  twenty- 
eighth  day.  The  last  are  less  highly  developed  than  the 
first,  and  while  the  lower  ones  are  forming  the  upper  ones 
are  undergoing  metamorphosis  into  their  adult  structures. 

The  changes  that  occur  in  the  VISCERAL  ARCHES  will  be 

318 


VISCERAL   ARCHES.  319 

considered  first:  Each  arch  consists  of  a  core  of  mesoderm 
containing  a  rod  of  cartilage  and  a  blood-vessel  called  the 
visceral  arch  vessel;  externally  the  arch  is  covered  by 
ectoderm  and  internally  by  entoderm.  The  arches  are 
separated  from  each  other  by  a  groove  or  depression,  inter- 
nally, and  externally,  and  spanning  the  groove  is  the  vis- 
ceral cleft  membrane  consisting  merely  of  ectoderm  and 
entoderm,  so  that  no  real  complete  cleft  exists  in  the  early 
stages  of  development;  in  aquatic  animals  these  membranes 
do  rupture  to  form  the  gill-clefts.  On  each  side  there  are 
four  external  and  four  internal  visceral  grooves  or,  better, 
branchial  pouches. 

The  first  arch,  as  previously  mentioned,  divides  into  two 
portions,  maxillary  and  mandibular;  the  maxillary  part 
unites  with  naso-frontal  process  to  complete  the  upper  jaw; 
it  itself  gives  rise  to  the  bulk  of  the  upper  jaw  and  most 
of  the  palate.  The  upper  jaw  is  completed  by  about  the 
fortieth  to  the  forty-seventh  day.  The  mandibular  process 
unites  with  its  fellow  of  the  opposite  side  to  form  the 
complete  lower  jaw,  union  being  completed  by  the  end  of 
the  fifth  week,  or  thirty-fifth  day.  In  addition,  the  cartilage 
of  the  mandibular  process  gives  rise  to  incus  and  malleus, 
and  stylomandibular  ligament. 

The  rod  of  cartilage  of  the  second  arch  gives  rise  to  the 
stapes,  styloid  process,  stylohyoid  ligament  and  lesser 
cornu  of  the  hyoid  bone. 

The  cartilage  of  the  third  arch  forms  the  body  and  greater 
cornu  of  the  hyoid  bone. 

The  cartilages  of  the  fourth  and  fifth  arches  unite  and 
form  a  single  mass,  the  thyroid  cartilage  of  the  larynx. 

The  first  external  branchial  pouch  persists  only  at  its 
dorsal  end  to  form  here  the  external  auditory  canal. 
From  both  first  and  second  arches  in  this  region  the  ear  is 
developed.  The  remaining  pouches  are  lost  as  the  arches 


320         DKVKLOPMKNT  OF  I'AC'K  AND  TEETH. 

overlap  each  other  from  above  downward.  Occasionally 
part  of  a  pouch  persists  as  an  enclosed  cyst  of  ectoderm 
and  this  is  called  a  branchial  cyst.  In  case  a  pouch  mem- 
brane ruptures  and  permits  of  a  passage-way  from  the  out- 
side to  the  gut-tract  it  is  called  a  cervical  fistula. 

The  first  internal  pouch  is  formed  into  a  tube  with  its 
outer  end  dilated  into  an  irregular  cavity,  the  tympanic 
cavity;  the  tube-like  portion  connecting  this  with  the 
pharynx  is  called  the  Eustachian  tube.  That  part  of  the 
first  pouch  membrane  separating  the  external  auditory 
canal  from  the  tympanic  cavity  is  the  future  tympanic 
membrane,  or  ear  drum.  In  the  middle  of  the  ventral 
portion  of  the  first  pouch  is  found  a  projection,  the  tuber- 
culum  impar,  which  later  becomes  the  anterior,  or  apical 
two-thirds  of  the  tongue. 

From  the  region  of  the  second  pouch  (representing 
second  and  third  arches)  we  find  the  tonsil  and  lateral 
recess  of  the  pharynx  developed,  dorsally,  while  ventrally 
in  the  median  line  the  middle  lobe  of  the  thyroid  body  is 
formed,  and  just  lateral  of  this  the  dorsal,  or  basal  one- 
third  of  the  tongue  by  two  masses  (one  on  each  side). 

In  the  third  pouch  region  (third  and  fourth  arches) 
the  thymus  body,  as  two  lobes,  appears  and  also  the  inferior 
parathyroids  and  the  carotid  bodies. 

From  the  fourth  pouch  (fourth  and  fifth  arches)  the 
lateral  lobes  of  the  thyroid  body  with  the  superior  para- 
thyroids. 

The  NASO-FRONTAL  PROCESS  is  at  first  a  blunt  mass  of 
tissue  projecting  from  che  frontal  region.  As  it  grows 
down  between  the  maxillary  divisions  of  the  first  visceral 
arch,  it  becomes  thickened  along  its  margins,  forming  here 
the  globular  processes;  each  process  contains  a  little  depres- 
sion that  constitutes  the  nasal  pit.  In  addition,  two 
masses,  the  lateral  nasal  processes,  develop  from  the 


NASO-FRONTAL    PROCESS. 


32I 


naso-frontal  process,  at  the  orbital  region,  to  form  the 
lateral  boundary  of  the  nasal  pits.  Usually  by  the  fortieth 
or  forty -second  day  the  naso-frontal  process  has  filled  the 
gap  between  the  two  maxillary  processes  of  the  first  arch, 
and  union  of  these  parts  is  completed.  As  a  result  the 
nasal  pits  are  separated  from  the  mouth  cavity.  The 
derivatives  of  the  naso-frontal  process  are  the  middle  of  the 


FIG.  105. — FACE  OF  AN  EMBRYO  OF  8  MM.  (McMurrich,  after  His), 
pg,  Globular  process  of  naso-frontal  process;  np,  nasal  pit  bounded  exter- 
nally by  the  lateral  nasal  process;  os,  oral  pit;  mxp,  maxillary  process  of 
first  visceral  arch. 

upper  jaw  (intermaxillary  bones)  the  middle  of  the  upper 
lip,  the  tip,  septum,  alae  and  briuge  of  the  nose  and  the 
vomer.  The  crevice  between  lateral  nasal  processes  and 
the  maxillary  division  of  the  first  arch  extends  from  the 
orbit  to  the  nose  cavity.  When  this  crevice  is  closed  a 
cord  of  epithelium  is  inclosed,  and  by  hollowing  out  this 
cord  of  cells  forms  the  naso-lacrimal  duct.  If  the  lip  por- 


322        DEVELOPMENT  OF  FACE  AND  TEETH. 

tions  of  the  naso-frontal  process  and  first  arch  fail  to  unite, 
a  malformation,  unilateral ,  or  bilateral  hare-lip,  is  produced. 
If  the  bony  parts  within  are  affected,  various  forms  of  cleft- 
palate  result. 

The  palate  is  developed  in  the  form  of  three  shelves,  two 
lateral  from  the  maxillary  processes  of  the  first  arch  and 
one  frontal,  triangular,  from  the  naso-frontal  process. 

At  about  the  eighth  week  union  between  the  lateral 
shelves  at  the  front  end  and  the  naso-frontal  portions  be- 
gin; by  the  ninth  week  union  as  far  as  the  posterior  border 
of  the  future  hard  palate  is  completed,  by  the  eleventh 
week  the  soft  palate  is  finished  and  by  the  end  of  the  third 
month  the  uvula  is  complete.  Various  malformations 
may  occur  here,  as  partial,  or  complete  cleft-palate  and 
bifid  uvula.  Then  after  the  upper  jaw  is  completed  two 
ridges  appear  upon  each  jaw,  the  inner  represents  the  gum 
and  the  outer  the  lip. 

The  Teeth. — The  teeth  are  developed  partially  (enamel) 
from  the  ectoderm  and  partially  (dentin,  cementum,  pulp, 
and  peridental  membrane)  from  the  mesoderm. 

There  are  two  sets  of  teeth  in  the  mammals,  TEMPORARY, 
or  DECIDUOUS,  or  MILK  TEETH,  and  PERMANENT,  or  suc- 
CEDANEOUS  TEETH.  Such  animals  are  diphyodonts.  Ani- 
mals that  may  develop  teeth  successively  without  regard 
to  number  are  polyphyodonts. 

In  the  former  case  the  teeth  are  unlike,  and  the  animals 
are  heterodonts,  while  in  the  latter  case  the  teeth  are  all 
alike  and  the  class  is  that  of  homodonts. 

The  teeth  begin  to  develop  during  the  sixth  -week 
(shortly  after  the  completion  of  the  lower  jaw).  From 
the  under  surface  of  the  thickened  epithelium  of  the  jaw 
a  band  of  epithelial  cells  grows  into  the  mesodermal  core 
of  the  jaw.  This  is  the  DENTAL  SHELF,  the  earliest  indica- 
tion of  the  developing  teeth.  Shortly  after  the  formation 


THE    TEETH. 


323 


Ill^fpP^* 


FIG.  1 06 — FOUR  STAGES  OF  TOOTH  DEVELOPMENT 
(After  Bohm,  Davidoff  and  Huber). 

A,  Formation  of  the  enamel  from  the  dental  shelf;  B,  later  stage  with  early 
formation  of  the  dental  papilla;  C,  later  stage  showing  enamel  sac  with 
its  layers  differentiating  and  the  dental  paiplla  well  advanced;  D,  enamel 
sac  completed  (just  preceding  enamel  formation)  connected  to  dental 
shelf;  dental  papilla  completed,  i,  i,  i,  i,  oral  epithelium;  2,  2,  2,  2, 
basal  layer  of  same;  3,3,3,  3,  mesoderm  of  jaw;  4,  4,  4,  4,  outer  layer  of 
enamel  organ;  5,  5,  5,  5,  middle  layer;  6,  6,  6,  inner  layer;  7,  7,  7,  dental 
papilla;  8,  layei  of  odontoblasts;  9,  dental  shelf;  10,  follicular  sheath. 


324        DEVELOPMENT  OF  FACE  AND  TEETH. 

of  this  shelf  the  epithelium  at  the  area  of  thickening  sinks 
in  forming  the  dental  groove.  The  dental  shelf  extends 
from  one  end  of  the  jaw  to  the  other  and  leans  toward 
the  median  plane  of  the  head,  and  from  the  outer  free  or 
labial  surface  ten  little  germs  or  buds  develop,  called  the 
ENAMEL  GERMS.  There  are  ten  in  each  jaw,  and  they 
represent  enamel  organs  of  the  temporary  teeth.  These 
buds  appear  successively:  those  for  the  central  incisors 
first,  then  lateral  incisors,  first  molars,  canine,  and  second 
molars.  The  earliest  buds  appear  during  the  seventh  or 
eighth  week.  The  enamel  bud  is  at  first  flask-shaped,  and 
its  connection  with  dental  shelf  becomes  smaller.  Gradu- 
ally the  surface  opposite  to  the  dental  shelf  connection  be- 
comes invaginated  by  condensing  mesoderm;  the  con- 
cavity deepens  and  a  sac  is  thus  formed,  while  at  the  same 
time  the  dental  shelf  connection  becomes  more  attenuated. 
The  sac  consists  of  three  layers,  inner,  middle,  and  outer. 
The  mass  of  condensed  mesoderm  that  has  caused  the  sac 
formation  of  the  enamel,  but  which  lies  now  in  the  enamel 
sac,  constitutes  the  dental  papilla.  During  about  the 
tenth  week  mesoderm  in  the  immediate  neighborhood  of 
the  enamel  sac  condenses  to  form  a  sheath  for  the  whole 
structure,  and  this  is  called  the  dental  follicle.  Meanwhile 
the  dental  shelf  becomes  attenuated  and  tends  to  disappear. 

The  succeeding  changes  will  be  described  under  Enamel 
Formation,  Dentin  Formation  and  Cementum  Formation. 

Enamel  Formation. — The  enamel  organ  now  consists 
of  three  layers:  the  OUTER  LAYER  is  composed  of  simple 
columnar  epithelial  cells  continuous  with  the  inner  layer  of 
cells  at  the  base  of  the  organ.  They  play  no  part  in  the 
formation  of  enamel.  The  MIDDLE  LAYER  consists  of  a  mass 
of  stellate  cells  varying  in  thickness  as  Fig.  107  shows; 
these  cells  make  up  the  bulk  of  the  enamel  organ  and  the 
meshwork  formed  by  them  is  filled  with  a  fluid.  This 


ENAMEL    FORMATION. 


325 


layer  likewise  has  nothing  to  do  with  the  direct  formation 
of  enamel,  but  seems  to  have  a  nutrient  function.  Along 
the  innermost  portion  of  this  reticular  mass  is  a  group  of 


FIG.  107. — SECTION  OF  A  DEVELOPING  TOOTH  OF  A  CAT  EMBRYO. 

(After  Pier  sol.} 

A,  Outer,  B,  middle,  C,  inner  layers  of  enamel  organ;  D,  formed  enamel; 
E,  formed  dentin;  F,  layer  of  odontoblasts;  Gy  follicular  sheath;  H, 
dental  papilla,  mesoderm 

cells  forming  a  layer  called  the  STRATUM  INTERMEDIUM. 
This  layer  consists  chiefly  of  spherical  cells  mixed  with 
some  columnar  elements.  Apparently  the  spherical  cells 
have  elongated  to  the  columnar  type,  probably  for  the 


326        DEVELOPMENT  OF  FACE  AND  TEETH. 

purpose  of  replacing  cells  that  fail  in  the  innermost  layer. 
This  stratum  intermedium  is  looked  upon  as  the  reserve 
layer  to  the  enamel-forming  cells;  the  cells  of  this  stratum 
are  most  numerous  where  enamel  formation  is  most  active. 

The  INNER  LAYER  is  composed  of  a  single  row  of  tall 
slender,  columnar  elements;  these  form  a  closely  packed 
unbroken  layer  surrounding  the  dental  papilla  and  are 
termed  the  ameloblasts.  The  nuclei  lie  in  the  peripheral 
portion  of  the  cells. 

Enamel  deposition  begins  during  the  sixteenth  week  of 
intrauterine  life,  in  the  temporary  teeth.  According  to 
Tomes  and  others,  the  inner  ends  of  the  enamel  cells  become 
calcified  and  converted  directly  into  enamel.  An  organic 
matrix  is  formed  in  which  the  enamel  is  deposited,  probably 
in  the  form  of  calcoglobulin  globules.  The  organic  matter 
disappears,  leaving  the  homogeneous,  inorganic  material 
representing,  no  doubt,  the  fused  globules  of  calcoglobulin. 
According  to  Andrews  and  others,  the  enamel  is  secreted 
from  the  cell  in  some  form  (calcoglobulin) ,  and  this  solidifies 
and  forms  outside  of  the  cell.  The  first,  however,  seems 
to  be  the  more  acceptable  explanation.  Enamel  is  formed 
from  within  outward,  so  that  the  youngest  enamel  is  upon 
the  surface  while  the  oldest  is  next  to  the  dentin. 

Capillary  blood-vessels  have  been  noted  in  the  enamel 
organ  by  Bromell.  It  seems  that  before  calcification  be- 
gins that  vessels  are  absent;  with  the  formation  of  enamel 
vascularization  of  the  enamel  organ  begins  and  is  said  to 
persist  until  the  tooth  erupts.  By  the  time  that  the  tooth 
begins  to  erupt,  or,  at  the  latest,  when  completely  erupted, 
the  enamel  is  fully  formed. 

Between  the  enamel  organ  and  the  surface  of  the  dentinal 
papilla  is  a  layer  of  homogeneous  substance  called  the 
membrana  preformativa.  Reference  to  this  will  be  made 
later. 


DENTIN    FORMATION.  327 

Dentin  Formation. — The  dentin  is  derived  from  the 
dental  papilla;  this  structure  is  composed  of  embryonic 
connective  tissue  in  which  four  different  kinds  of  cells  are 
found.  Upon  the  surface  of  the  papilla  will  be  found  a 
single  layer  of  flask-shaped  cells,  the  odontoblasts.  These 
form  the  membrana  eboris  from  which  the  dentin  is  derived. 
The  basal  portion  of  each  cell  is  directed  toward  the  papilla, 
or  centrally,  and  contains  the  nucleus.  Each  cell  possesses 
processes;  those  which  are  directed  toward  the  enamel 
organ  constitute  the  ultimate  dental  fibres.  These  cells  are 
differentiated  shortly  before  the  formation  of  dentin  begins. 
Just  beneath  the  layer  of  odontoblasts  the  papilla  is 
practically  devoid  of  cells;  beneath  this,  however,  there  is  a 
cellular  area  of  mixed  cells  and  then  again  a  central  area 
containing  but  few  cells. 

Dentin  is  first  formed  at  the  cutting,  or  occlusal  surface 
and  during  the  sixteenth  week  of  intrauterine  life.  The 
dentin  seems  to  be  a  secretion  from  the  peripheral  ends  of 
the  odontoblasts  so  that  the  processes  in  this  region  are 
surrounded  by  the  lime  salts,  thus  forming  the  dental 
sheaths  and  tubules;  the  odontoblasts  are  constantly  out- 
side of  the  dentin  that  is  formed.  The  dentin  is  laid  down 
from  without  inward,  and  in  areas  where  dentin  formation  is 
incomplete  spaces,  that  are  called  the  interglobular  spaces, 
remain.  As  the  dentin  becomes  thicker  (by  encroach- 
ment upon  the  dental  papilla)  the  dental  fibres  elongate 
and  the  tubules  become  correspondingly  longer.  The 
dentin  in  the  crown  portion  is  formed  first,  the  root  portion 
being  completed  last.  When  the  teeth  begin  to  erupt 
their  roots  are  partially  formed;  by  the  time  that  the  whole 
crown  is  exposed  the  fang  is  usually  completed.  In  the 
case  of  the  incisor  teeth  the  roots  are  usually  completed  by 
the  time  that  the  tooth  begins  to  erupt. 

Cementum  Formation. — The  cementum  is  also  of  mesoder- 


328        DEVELOPMENT  OF  FACE  AND  TEETH. 

mal  origin.  As  the  enamel  organ  becomes  in  vagina  ted  by 
the  dental  papilla  the  mesoderm  immediately  surrounding 
the  enamel  organ  condenses  to  form  a  sac-like  covering,  the 
DENTAL  FOLLICLE.  This  structure  gives  rise  to  the  cemen- 
tum  and  the  alveolar  process  of  the  jaw  and  its  remains 
constitute  the  PERIDENTAL  MEMBRANE.  The  follicle  is 
formed  shortly  after  the  tenth  week.  During  the  earlier 
stages  of  development  the  dental  follicle  covers  the  entire 
enamel  organ  and  is  connected  with  the  dental  papilla  at 
its  base.  The  follicle  upon  its  outer  surface  forms  bone, 
and  upon  its  inner  surface  forms  the  cementum  of  the  tooth. 
As  the  enamel  organ  grows  the  follicle  seems  to  recede  from 
the  cutting  edge  until  the  neck  portion  is  reached;  at  this 
point  it  remains,  and  as  the  root  is  formed  by  the  dental 
papilla  the  follicle  forms  the  cementum  until  the  full 
length  of  the  root  is  reached.  The  process  of  cementum 
formation  is  like  that  of  bone,  a  secretion,  and  layer  are 
formed  as  described  in  the  section  on  the  structure  of 
cementum.  The  cementum  and  bone  of  the  jaw  are  de- 
veloped from  the  dental  follicle,  or  peridental  membrane,  at 
the  expense  of  the  latter,  it  becoming  thinner  as  the 
cementum  and  alveolar  bone  increase  in  thickness. 

The  temporary  teeth  begin  to  erupt  from  the  sixth  to  the 
eighth  month  after  birth  and  the  set  is  usually  completed 
by  the  twenty-fourth  to  the  thirtieth  or  thirty-sixth  month. 
The  order  of  eruption  is  as  follows: 

Central  incisors,  sixth  to  eighth  month. 

Lateral  incisors,  seventh  to  ninth  month. 

First  molars,  twelfth  to  fourteenth  month. 

Canines,  sixteenth  to  eighteenth  month. 

Second  molars,  twenty-fourth  to  thirty-sixth  month. 

The  permanent  teeth  are  thirty-two  in  number.  The 
difference  in  number  of  the  two  sets  and  later  appearance 


THE    PERMANENT    TEETH.  329 

of  added  teeth  is  due  to  the  fact  that  the  jaw  at  certain 
periods  will  accommodate  only  a  certain  number  of  teeth, 
and  any  attempt  to  hurry  their  appearance  will  interfere 
with  the  dental  arch.  Of  these  permanent  teeth,  the 
molars,  twelve  in  number,  are  not  succedaneous  teeth  at  all, 
but  primary  teeth  as  will  be  explained  later.  The  germs  for 
most  of  the  permanent  teeth  are  formed  during  intrauterine 
life. 

During  the  sixteenth  week  a  bud  appears  at  each  end 
of  the  dental  shelves;  these  buds  are  the  germs  for  the  first 
permanent  molar  teeth.  During  the  seventeenth  week  the 
germs  for  the  central  incisors  appear  from  the  lingual  sur- 
face of  the  dental  shelf,  opposite  the  point  of  formation 
of  the  corresponding  temporary  tooth;  the  remaining  suc- 
cedaneous teeth  follow  in  order  of  their  eruption.  The 
enamel  organs  undergo  the  same  changes  as  previously 
described,  with  the  exception  that  the  process  is  somewhat 
slower,  making  their  eruption  somewhat  later.  As  was 
stated  above,  the  germs  for  the  first  permanent  molars 
appear  at  the  ends  of  the  dental  shelves  and  so  have  no 
forerunners;  the  germs  for  the  second  molars  are  developed 
from  the  neck  of  the  enamel  organs  of  the  first  molar  during 
the  third  to  the  fifth  month  after  birth;  the  enamel  sacs  for 
the  third  permanent  molars  appear  from  the  neck  of  the 
enamel  sacs  of  the  second  molars  during  the  third  to  the 
fifth  year  after  birth.  All  of  the  molar  teeth,  therefore, 
have  no  forerunners,  and,  are  then,  primary  and  not  suc- 
cedaneous teeth. 

The  first  permanent  molar  tooth  is  the  first  one  of  the 
second  set  to  appear;  the  order  and  times  are  as  follows: 

First  molar,  sixth  year. 
Central  incisors,  seventh  year. 
Lateral  incisors,  eighth  year. 


330        DEVELOPMENT  OF  FACE  AND  TEETH. 

First  premolars,  ninth  year. 
Second  premolars,  tenth  year. 
Canines,  eleventh  to  twelfth  year. 
Second  molars,  twelfth  to  thirteenth  year. 
Third  molars,  seventeenth  to  twenty-fifth  year. 

The  eruption  and  succession  of  the  teeth  are  by  no  means 
simple  processes.  As  the  tooth  germs  develop  they  at  first 
lie  in  a  groove  of  the  jaw,  covered  merely  by  the  gum; 
gradually  transverse  partitions  of  bone  form  so  that  the 
entire  tooth  is  ultimately  incased  in  the  bone  of  the  jaw. 
The  bone  intervening  between  the  tooth  and  the  gum 
amounts  to  but  a  thin  lamella  that  is  completed  shortly 
before  the  tooth  is  to  erupt,  except  in  the  region  where 
the  gubernaculum  passes  to  the  gum.  As  eruption  is  to 
take  place,  that  bone  which  is  last  formed  (toward  the 
gum)  is  resorbed  so  that  there  is  no  interference  with 
eruption. 

The  process  of  eruption  is  as  follows:  The  bone  covering 
the  labial  surface  of  the  crown  is  resorbed  until  fully  one- 
half  of  the  surface  is  exposed;  this  is  followed  by  the  re- 
sorption  of  the  bone  on  the  lingual  surface  but  here  the 
process  is  slower  and  less  complete,  leaving  some  bone  to 
protect  the  germs  of  the  permanent  teeth  underneath.  As  a 
result  of  this  process  the  crown  apparently  grows  through 
the  gum  when  in  reality  the  gum  becomes  stretched  over 
the  tooth  by  the  disappearance  of  the  bone  beneath.  As 
the  resorption  continues  until  the  crown  is  exposed  new 
bone  is  laid  down  about  the  base  of  the  tooth  to  strengthen 
its  position.  According  to  some  writers  the  tooth  erupts 
by  the  growth  of  the  root  forcing  the  crown  above  the  gum 
surface.  When  one  considers  that  in  the  temporary  and 
permanent  cuspid  teeth  the  roots  are  completed  by  the 
time  eruption  occurs,  this  force  cannot  be  counted  upon  as  a 


THE    PERMANENT    TEETH.  331 

factor  in  the  eruption  of  the  teeth.  It  might  play  some 
part  in  the  eruption  of  the  other  teeth,  but  even  this  is 
doubtful. 

From  the  eruption  of  the  second  temporary  molar  tooth 
until  the  fourth  year  the  teeth  are  practically  quiescent. 
From  the  fourth  year  on  the  temporary  teeth  begin  to 
decalcify  and  drop  out  to  make  room  for  the  permanent 
teeth.  The  process  of  decalcification  is  one  of  absorption; 
it  begins  in  the  apical  portion  of  the  tooth  and  advances  to 
the  enamel  line.  The  central  incisors  are  the  first  af- 
fected, at  about  the  fourth  year,  and  the  others  follow  in 
order  of  their  eruption.  As  a  result  of  this  process  the  root 
becomes  absorbed  and  the  hold  of  the  tooth  upon  the  jaw 
becomes  weakened;  ultimately  merely  an  enamel  cap 
remains;  this  process  extends  over  a  period  of  about  three 
years  for  each  tooth,  going  on  simultaneously  or  success- 
ively in  the  various  teeth.  Some  claim  that  the  process  of 
resorption  of  the  roots  is  due  to  the  pressure  exerted  upon 
the  root  by  the  permanent  tooth  beneath.  This  does  not, 
however,  seem  to  be  the  cause,  for  in  cases  of  absence  of  the 
succedaneous  tooth  the  process  of  absorption  of  the  root 
of  the  temporary  tooth  occurs  as  usual. 

The  permanent  teeth  follow  the  temporary  successively 
as  the  latter  are  lost.  As  the  jaw  gradually  increases  in 
length  there  is  a  second  permanent  molar  added  at  the 
twelfth  to  the  fourteenth  year  and  a  third  one  at  the  eigh- 
teenth to  the  twenty-fifth  year. 

The  permanent  teeth  erupt  in  the  same  manner  as  the 
temporary  organs;  that  is,  by  the  absorption  of  the  bone 
from  the  crown  portion.  As  this  process  of  absorption  occurs 
during  the  eruption  of  both  sets  the  jaws  would  become 
thinner  from  above  downward;  to  offset  this  nature  adds 
below  more  than  is  absorbed  above  so  that  the  dimension 
from  above  downward  increases  up  to  the  prime  of  life. 


332        DEVELOPMENT  OF  FACE  AND  TEETH. 

As  the  second  set  is  gradually  lost  bone  is  not  replaced  as 
rapidly  as  lost  so  that  in  an  old  jaw  the  alveolar  processes 
are  lost  (showing  the  absorption  from  above  downward) 
and  the  vertical  dimension  decreases. 

Connected  with  the  permanent  tooth  is  a  structure,  the 
GUBERNACULUM  DENTis,  that  seems  to  be  of  importance. 
It  is  a  fibrous,  cord-like  structure  attached  to  the  apex  of 
the  tooth-sac  and  ends  at  the  epithelium  of  the  gum.  It 
seems  to  direct  the  follicle  by  its  tension  and  also  to  indicate 
the  direction  of  eruption,  and  to  maintain  the  tooth  in 
position. 

In  regard  to  malformation  of  the  teeth,  both  sets  may 
fail  to  appear,  or  the  succedaneous  teeth  alone  may  not 
develop;  again  individual  teeth  may  be  absent,  or  a  third 
set  may  appear  after  the  second  has  been  lost.  What  is 
more  common  than  the  latter  is  a  duplication  of  some  of 
the  permanent  teeth  forming  a  row  within  the  normal  set; 
a  fourth  molar  may  appear  if  the  jaw  is  long  enough  to 
accommodate  it.  Malformations  of  the  root  may  be  in  the 
form  of  an  additional  root  or  the  fusion  of  several  to  form 
one  massive  root.  Again,  the  teeth  may  be  united  by 
fusion  (if  before  birth)  or  concrescence  (if  after  birth).  If 
two  teeth  are  found  in  a  single  sac  the  condition  is  known 
as  geminous  teeth. 


INDEX. 


Accessory  cavities,  312 
Acervulus  cerebri.  252 
Achromatic  spindle,  39 
Achromatin,  33 
Acid  cells,  14.  135 
Acidophil,  see  Eosinophil 
Acrosome,  191 
Adelomorphous  cells,  137 
Adipose  tissue,  64 
Adrenal,  183 
Adventitia  of  artery,  99 

of  vein,  103 
Agminated  follicles,  66 
Air-sacs,  166 
Albumen,  Mayer's,  28 
Alcohol     for     clearing,     absolute     and 
ether,  9 

for  fixation,  absolute,  4 

absolute  and  ether,  5 

absolute  and  formalin,  5 

ninety-five  per  cent.,  5 
Alimentary  tract,  118 
Allantois,  221 
Alum  carmin,  15 
Alvei,  1 66 
Alveolar  ducts,  166 
Alveoli  of  lungs,  166 
Alveolo-tubular  glands,  55 
Amakrine  cell,  285 
Ameboid  motion  of  leukocytes,  106 
Ameloblasts,  326 
Amitosis,  36 
Amnion,  false,  219 

true,  226 
Amniotic  cavity,  219 

folds,  219 
Amphipyrenin,  33 
Ampullae 

capillary,  102 

of  ear,  303 

of  oviduct,  208 

of  spleen,  116 
Amyloid  bodies,  196 
Anabolism,  35 
Anaphase,  39 
Anastomoses,  102 
Angle  of  infiltration,  281 
Angles,  leaden,  7 
Anilin  oil-xylol,  23 
Anisotropic  disc,  77 
Annuli  fibrosi,  96 
Annulus  fibrosus,  299 
Antrum  of  follicle,  202 
Aortic  bodies,  no 


Appendix,  follicles  of,  144 

glands  of,  144 

occlusion  of,  145 
Aqueous  humor,  288 
Arantii,  corpus,  97 
Arachnoid,  245 

Arches,  visceral,  318,  319,  320 
Arcuate  fibres  of  the  pons,  263 
Arcus  tarseus  externus,  295 

internus,  295 
Area  of  Langerhans,  156 
Areola,  243 
Areolar  tissue,  64 
Arrectores  pilorum,  237 
Arteries,  large,  100 

medium,  99 

small,  101 
Astrocyte,  86 
Astrosphere,  34 
Atria,  166 

Atrio ventricular  bundle,  97 
Attraction  sphere,  33 
Auditory  hairs,  303 

nerve,  309 

ossicles,  299 

teeth,  306 

Auerbach,  plexus  of,  146 
Axial  fibre,  192 
Axis-cylinder,  84 
Axilemma,  87 

Basal  border,  144 
Balsam,  23 

Basement  membrane,  50 
Basic  stains,  12 
Basilar  membrane,  306 
Basket  cells,  254 
Basophil,  107,  108 
Belly-stalk,  220 
Bensley's  solution,  3 
Benzol,  7,  22 
Berlin  blue,  24 
Bertin,  columns  of,  173 
Bile  capillaries,  150 
Bipolar  cells,  85 
Bismarck  brown,  14 
Bladder,  180 
Blastodermic  vesicle,  42 
Blastula,  40,  217 
Blind  spot,  286 
Blocking,  8 
Blood 

cells  of,  erythroblasts,  26,  106 
erythrocytes,  104 


333 


334 


INDEX. 


Blood 

cells  of,  leukocytes,  106 

platelets,  26,  108 
crystals,  32 
films,  25 
fixation,  26 
hemoglobin,  105,  109 
platelets,  26,  108 
technic,  fixation,  26 

spreads,  26 

stains,  16,  26,  27 
Blood-forming  organs 
carotid  gland,  no 
coccygeal  gland,  109 
hemolymph  nodes,  no 
marrow,  73 
Blood-vessels 
arteries,  99 
capillaries,  101 
heart,  98 
nerves  of,  100 
veins,  103 
Bone 

canaliculi,  72 
cells,  70 
compact,  70 
composition,  70 
corpuscles,  69 
decalcification,  n 
development 

endochondral,  74 

endosteum,  70 

growth,  77 

intramembranous,  77 
Haversian  canal,  70 

lamellae,  71 

system,  70 
lacunas,  72 

Howship's,  71 
lamellae,  70 
lymphatics  of,  74 
marrow  cavity,  72 

cells,  73 

red,  73 

yellow,  73 

nerves  of,  74 
osteoblasts,  69 
osteoclasts,  73 
perichondral,  74 
periosteum,  69 
Sharpey's  fibres  of,  69 
structure  of,  69 
Volkmann's  canals,  71 
vessels  of,  74 
Bone-cells,  70 
Bone-marrow 
cells  of,  73 
red,  73 
serous,  73 
yellow,  73 
Bones  of  ear,  99 
Bony  cochlea,  303 
labyrinth,  301 
Borax  carmin,  14 
Boundary  zone  of  choroid,  277 

of  kidney,  173 
Bowman's  capsule,  173 
glands,  312 


Bowman's  membrane,  275 
Brain,  see  Cerebrum 

sand,  252 
Bronchi,  163 
Bronchiole 

respiratory,  165 

terminal,  165 
Bruecker's  lines,  78 
Brunner's  glands,  142 
Bulb,  hair,  235 
Bulbus.oculi,  see  Eyeball 
Bundle  of  His,  97 
Burdach's  columns,  270 

Cajal,  cells  of,  247 
Calyces,  180 
Cambium  layer,  77 
Canada  balsam,  23 
Canal,  hyaloid,  288 

of  Petit,  259 

of  Schlemm,  281 

of  Stilling,  288 

of  spinal  cord,  267 

semicircular,  303 
Canaliculi,  of  bone,  72 

of  eyelid,  296 
Canalized  fibrin,  226 
Capillaries,  bile,  150 

blood,  101 

lymph,  112 

secretory  of  acid  cells,  136 
of  demiliunes,  158 
of  hepatic  cells,  150 
of  parotid,  155 
Capsule 

of  Bowman,  173 

of  Glisson,  148 

of  lens,  288 

of  Tenon,  297 

suprarenal,  183 
Carbol-xylol,  22 
Cardia,  136 
Cardiac  muscle,  82 
Carmin,  borax,  15 

alum,  15 

injection  mass,  24 
Carminic  acid,  16 
Carotid  gland,  no 
Cartilage 

calcification  of,  74 

capsule,  67 

cells,  67 

chrondroblasts,  67 

costal,  68 

elastic,  69 

fibro,  68 

hyalin,  67 

ossification  of,  74 

perichondrium,  66 

vessels  of,  69 
Caruncle,  lacrimal,  295 
Cauda  equina,  263. 
Cecum,  foramen,  127 
Cedar  oil,  6,  22 
Cell,  the,  31 
Cellodin  infiltration,  9 
Cells 

acid,  14,  35 


INDEX. 


335 


Cells 


acidophilic,  107 
adelomorphous,  134 
amakrine,  285 
basket,  254 
basophilic,  107 
bipolar,  85 
blood 

red,  104 

white,  105 
bone,  70 
Cajal,  247 
cartilage,  67 
centro-acinar,  155 
chief,  134 

chromaffin,  184,  251 
ciliated,  48 
Claudius,  306 
columnar,  47 
cone- visual,  282 
connective  tissue,  59 
crystals  (eye),  278 
decidual,  206 
definition  of,  31 
Deiter's  86,  309 
delomorphous,  135 
egg,  40 

ectodermal,  218 
enamel,  325 
endothelial,  51 
entodermal,  218 
endymal,  267 
epithelial,  245 
eosinophil,  107 
fat,  64 
form,  34 
follicular,  203 
ganglion,  89 
giant,  40 
glia,  79 

glycogen  in,  32,  150 
goblet,  49,  134,  138,  142 
granule  (cerebellum),  254 
Golgi,  86 
gustatory,  314 
hair,  302,  307 
Hensen's  306 
hepatic,  150 
interstitial, 

of  ovary,  201 

of  testicle,  189 
Langhans,  224 
liver,  150 
lutein,  206 
marginal,  238 
marrow,  73 
mast,  107 
mesothelial,  51 
mitral,  250 
mossy,  86 
mother,  174 
mucin,  49,  134 
multipolar,  86 
muscle 

cardiac,  82 

smooth,  8 1 

voluntary,  78 


Cells 

nerve,  84,  86 

neuro-epithelial,  50 

neuroglia,  86 

of  Claudius,  306 

of  Clark's  column,  266 

of  Golgi,  87 

of  Hensen,  306 

of  Langhans,  224 

of  Leydig,  189 

of  Purkinje,  254 

of  Sertoli,  189 

olfactory,  312 

oxyntic,  135 

parietal,  135 

peptic,  134 

pigmented,  48 

pillar,  307 

plasma,  59 

polymorphous,  249 

polynuclear,  107 

prickle,  48,  211 

properties  of,  34 

pseudostratified,  48 

pyramidal 
large,  247 
small,  249 

reproduction  of,  36 

rod-visual,  283 

seminiferous,  188 

sexual 

fertilization,  42 
maturation,  41,  205 

shape  of,  34 

size  of,  34 

spider,  86 

squamous,  45 

stain  reaction  of,  32 

structure  of,  3 1 

stellate  bone,  70 

connective  tissue,  59 

sustentacular 
of  ear,  301,  309 
of  olfactory  membrane,  311 
of  retina,  284 
of  taste-bud,  127,  314 

tactile,  90 

tendon,  61 

transitional,  49 

trophodermal,  219 

wandering,  59 
Cell-body,  31 
Cell-division 

a  mitosis,  36 

mitosis,  37 

time  of,  40 
Cell-knots,  224 
Cell-mass,  inner,  42,  217 

outer,  42,  217 
Cell  membrane  (wall),  34 
Celloidin 

casting,  9 

hardening,  10 

infiltration,  9 

sectioning,  n 

solutions,  9 
Cell-spaces  of  Nuel,  309 


336 


INDEX. 


Cementoblasts,  328 
Cementum 

formation  of,  327 

structure  of,  123 
Central  artery  of  retina,  289 

nerve  system,  245 

spindle,  39 

Centro-acinar  cells,  155 
Centrosomes,  33,  41 
Cerebellar  columns,  direct,  269 

cortex,  253 

basket  cells  of,  254 

capillaries  of,  272 

cells  of  Purkinje,  254 

ganglionic  layer,  254 

granule  layer,  254 

medullary  substance,  255 

molecular  layer,  254 

peduncles,  262 
Cerebral  cortex,  247 

capillaries  of,  272 

cells  of  Cajal,  247 

medullary  substance,  249 

molecular  layer,  247 

polymorphous  cells  of,  249 

pyramidal  cells  of,  247,  249 

radial  bundles,  249 

striations  of  Baillarger,  249 
of  Bechtereff,  249 

tangential  layer  of,  249 
Ceruminous  glands,  298 
Cervix,  210 
Chambers 

anterior,  289 

posterior,  289 

vitreous,  289 
Chief  cells,  134 
Chloroform  for  clearing,  7 
Chordae  tendineae,  97 
Chorio-capillaris,  278 
Chorion,  222,  226 

frondosum,  223 

laeye,  223 

primitive,  220 
Chorionic  villi,  223 
Choroid  coat 

arteries  of,  277 

boundary  zone,  277 

glassy  membrane,  278 

lamina  vasculosa,  277 

stroma  of,  276 

tapetum  cellulosum,  278 

fibrosum,  277 
Chromatic  spindle,  39 
Chromatin,  33 
Chromosomes,  38 

number  of,  38 
Chyli,  receptaculum,  146 
Cilia  of  eyelid,  294 
Ciliary  body,  278 

muscle,  279 

processes,  278 

ring,  278 
Ciliated  cells,  48 
Circulus  ridicus  major,  291 

minor,  291 

Circulatory  system,  96 
Circumferential  lamellae,  70 


Circumvallate  papilhc,  127 
Clark,  column  of,  269 
Claudius,  cells  of,  306 
Clearing 

blocks,  6 

sections,  22 
Clefts,  visceral,  319 
Clitoris,  196 
Coccygeal  gland,  109 
Cochlea 

bony,  303 

perilymph,  303 

spiral  ganglion  of,  310 
Cohnheim's  fields,  79 
Coiled  glands,  53,  298 
Colloid  substance,  169,  170,  251 
Colostrum  corpuscles,  243 
Columns 

of  Bertin,  173 

of  Sertoli,  189 

of  spinal  cord,  269 
Commissure,  gray,  267 

white,  268 
Compact  bone,  70 
Cone-fibres,  283 
Cone-granules,  283 
Coni  vasculosa,  188 
Conjunctiva 

corpuscles  of,  91,  295,  317 

palpebral,  295 

scleral,  274 
Connective  tissues 

adipose,  64 

areolar,  64 

blood,  77 

bone,  69 

cartilage,  66 

cells  of,  58 

classification  of,  58 

dentin,  77 

elastic,  62 

embryonic,  63 

fibrous,  58 

intercellular  substance  of,  59 

lymphoid,  65 

modified,  64 

mucous,  63 

origin  of,  59 

reticulum,  63 

retiform,  63 

varieties  of,  58 
Conus  medullaris,  263 
Convoluted  tubules  of  kidney,  174,  175 
Cord,  umbilical,  227 
Cords,  medullary,  113 
Corium,  231 
Cornea,  275 
Corneal  corpuscles,  275 

lacunae,  275 

Corneo-scleral  junction,  280 
Corona  radiata,  203 
Corpora  cayernosa,  198 
Corpus  albicans,  206 

Arantii,  97 

hemorrhagicum,  206 

Highmori,  186 

luteum  spurium,  206 
verum,  206 


INDEX. 


337 


Corpus  spongiosum,  199 
Corpuscles 

blood,  red,  104 
white,  1 06 

bone,  69 

colostrum,  243 

conjunct! val,  91,  317 

corneal,  275 

Smital,  91,  317 
assal's,  117 

Krause,  317 

lamellar,  91,  316 

Malpighian,  115 

Meissner's,  91,  315 

Pacinian,  91,  316 

renal,  173 

splenic,  115 

tactile,  90,  315 

Vater,  91,  316 

Wagner,  91,  315 

Corrosive  sublimate  fixative,  i,  2 
Corti's 

membrane,  309 

organ,  307 

tunnel,  307 
Cowper's  gland,  197 
Cotyledons,  226 
Creosote,  22 

Crescents  of  Gianuzzi,  158 
Crista  basilaris,  305 
Cristas  acusticae,  303 
Crossed  pyramidal  tract,  270 
Crown,  119 
Crypts,  gastric,  133 

Lieberkuehn's,  138 

tonsillar,  129 
Crystalline  lens,  288 
Crystals 

hematoidin,  108 

hemin,  109 

hemoglobin,  109 

in  the  choroid,  278 

Teichmann's,  109 
Cumulus  ovigerus,  202 
Cup,  imbedding,  8 
Cupola,  302 
Cuticular  border,  134 
Cuticle  of  hair,  236 
Cutis  vera,  231 
Cytoplasm,  31 


Dammar,  23 
Daughter  cells,  140 

nuclei,  40 

stars,  40 

Decalcification,  n 
Decidua 

ovular,  217,  220 

placental,  217 

reflexa,  217,  220 

serotina,  217 

uterine,  217 

vera,  217 
Decidual  cell,  226 
Dehydration,  5 
Deiter's  cells,  86,  309 
Delafield's  hematoxylin,  13 


Delomorphous  cells,  134 
Demilunes  of  Heidenhain,  158 
Dental  follicle,  324,  328 

groove,  324 

papilla,  324 

shelf,  322 
Dentin 

formation  of,  327 

structure  of,  107 
Dentinal  canals,  122 

fibres,  122 

tubes,  122 

sheaths,  120 

Derivatives  of  triploblast,  43 
Derma,  212 
Deutoplasm,  203 
Development  of  face,  318 

of  teeth,  322 
Diaster,  40 

Diffuse  lymph oid  tissue,  65 
Digestive  glands,  148 
Dilator  pupillae,  280 
Diphyodonts,  322 
Diploblast,  42,  218 
Direct  cell-division,  36 

cerebellar  tract,  269 

pyramidal  tract,  269 
Discus  proligerus,  202 
Dobie's  globules,  79 
Duct 

alveolar,  165 

Bartholin,  158 

cochlear,  303 

ejaculatory,  196 

endolymphatic,  301 

pancreatic,  156 

Rivini,  158 

Wharton's,  158 

Wirsungian,  156 
Duodenum,  142 
Dura,  245 

Ear 

external,  298 

internal,  300 

middle,  299 
Ear,  bones  of,  299 
Ear-stones,  302 
Ectoderm,  42,  218 

derivatives  of,  43 
Egg-tubes  of  Pflueger,  184 
Ehrlich-Biondi-Heidenhain  stain,  iO 
Ehrlich,  fixation  of  blood,  26 
Ejaculatory  duct,  196 
Elastic  cartilage,  69 

lamina  anterior,  275 
internal,  99 
external,  99 
posterior,  276 
Elastin,  62 

Ellipsoidal  sheaths,  116 
Embedding  celloidin,  9 

paraffin,  7 
Embryonic  area,  218 

shield,  219 

tissue,  62 
Emissary  veins,  199 


INDEX. 


Enamel,  120 

formation,  324 

organ,  324 

prisms,  120 
Endocardium,  96 
Endochondral  bone,  74 
Endolymph,  301 
Endomysium,  81 
Endoneurium,  89 
Endothelial  cells,  5 1 

membrane,  51 
End-plate,  95 
Endymal  cells,  268 
Entoderm,  42,  218 

derivatives,  43 
Entpdermal  vesicle,  218 
Eosin,  14 
Eosinophyl 

coarsely  granular,  107 

finely  granular,  107 
Epiblast,  41 
Epicardium,  98 
Epidermis,  230 
Epididymis,  190 
Epiglottis,  159 
Epimysium,  81 
Epineurium,  89 
Epiphysis,  252 
Epitendineum,  61 
Epithelium 

basal  border  of,  144 

ciliated,  48 

classification,  45 

columnar,  47 

cuticular  border  of,  138 

germinal,  201 

glandular,  50 

goblet,  9,  138,  142,  144 

modified,  46 

neuro-epithelial,  50 

of  mucous  membrane,  50 

pigmented,  50 

prickle,  48 

pseudostratified,  48 

respiratory,  166 

secretory  canals  of,  136,  150,  155 

squampus,  46 

transitional,  49 
Eponychium,  238 
Epoophpron,  208 
Equatorial  plate,  38 
Erectile  tissue,  198,  216 
Erlicki's  solution,  3 
Erythroblasts,  106 
Erythrocytes,  104 
Esophagus 

coats  of,  131 

glands  of,  132 

muscle  of,  132 

vessels  of,  133 
Eustachian  tube,  300 
Excretion,  35 
Exoplasm,  32 
External  ear,  298 
Eyeball 

angle  of  infiltration,  281 

blood-vessels  of,  289 

canal  of  Petit,  289 


Eyeball 

cnnal  of,  Schlemm    281 

Stilling,  288 
chambers  of,  289 
chproid,  276 
ciliary  body,  278 

muscle,  279 

processes,  278 

ring,  278 
cornea,  275 
hyaloid  canal,  288 
iris,  279 
lens,  288 

lymph  channels  of,  292 
optic  nerve,  287 
refractive  media,  288 
retina,  281 
sclera,  274 
venae  vorticosae,  291 
vitreous  humor,  288 
Eyelashes,  294 
Eyelid 

blood  supply,  295 
caruncle,  295 
cilia,  294 
conjunctiva,  295 
glands,  294 
lymphatics,  295 
nerves  of,  295 
plica  semilunaris,  295 
tarsus,  293 
third,  295 

Fallopian  tube,  208 
Farrant's  solution,  24 
Fascia,  62 
Fat,  64 

cells,  64 

crystals,  64 

stains  for,  65 

Female  genital  system,  201 
Fenestra  rotunda,  300 
Fenestrated  membrane  of  Henle,  101 
Ferrein,  pyramids  of,  172 
Fertilization,  42 
Fetal  circulation,  228 
Fibre-layer  of  Henle,  284 
Fibres 

cone,  283 

dentinal,  122 

Mueller's,  284 

muscle 

cardiac,  82 
intrafusal,  92 
smooth,  8 1 
voluntary,  78 

nerve,  amyelinated,  89 
myelinated,  87 

neuroglia,  87 

rod,  282 

Sharpey's,  69 
Fibro  cartilage,  68 
Fibrous  tissue,  58 
Filar  mass,  31 
Filiform  papillae,  126 
Films,  blood,  26 
Filum  terminale,  263 
Fimbriated  end  of  Fallopian  tube,  208 


INDEX. 


339 


Fissure  of  spinal  cord,  263 
Fixation,  i 

Fixatives,  see  Fixing  solutions 
Fixing  sections  on  slides,  28 
Fixing  solutions 

alcohol  absolute,  4 

absolute  and  ether,  5,  26 
absolute  and  formalin,  5,  26 
ninety-five  per  cent.,  5 

Bensley's,  3 

chromic  acid,  3 

Erlicki's,  3 

Flemming's,  3 

formalin,  4 

Golgi's,  4 

Heidenhain,  i 

Kopsch's,  3 

Mueller's,  2 

nitric  acid,  4 

Orth's,  3 

osmic  acid,  3 

potassium  bichromate,  2 

Tellyesnicky's,  2 

Zenker's,  2 

Flemming's  solution,  3 
Fluids,  see  Fixing  solutions 
Folds  of  Kerkring,  141 
Foliate  papillae,  314 
Follicles 

agminated,  66,  142 

Graafian,  201 

hair,  235 

lenticular,  134 

solitary,  66,  116 
Folliculi,  theca,  201 
Fontana,  spaces  of,  280 
Foramen  cecum,  127 
Foramina  nervosa,  310 
Formaldehyde,  4 
Formalin,  4 
Formative  yolk,  203 
Formatio  reticularis,  257,  262 
Fovea  centralis,  287 

Howship's,  71 
Freezing  tissue,  10 
Fungiform  papillae,  127 

Gall-bladder,  153 
Ganglia,  89 

spinal,  243 
Ganglion  cells,  89 

bipolar,  85 

multipolar,  86 

unipolar,  85 
Ganglion  spirale,  310 
Gastric  glands,  134 

pits,  133 

Gastrula,  42,  218 
Gelatin  injection  mass,  24 
Genital  corpuscles,  91,  317 

organs,  female,  201 

male,  186 
Genitalia,  215 
Germinal  center,  66 

epithelium,  201 

spot,  40,  203 

vesicle,  40,  203 
Germ-nucleus,  205 


Giant  cells,  40 
Gianuzzi,  crescents  of,  158 
Giraldes,  organ  of,  199 
Glacial  acetic  acid,  i 
Glands 

accessory  tear,  294 

alveolar,  55 

alveolo- tubular,  55 

arterial,  109 

Bartholin's,  215 

Bowman's,  312 

Brunner's,  142 

cardiac,  134 

carotid,  no 

ceruminous,  298 

coccygeal,  109 

coiled,  53 

Cpwper's,  197 

digestive,  148 

ductless,  57 

duodenal,  142 

excretory,  57 

fundus,  136 

intestinal,  138 

Krause's,  294 

labial,  118 

lacrimal,  296 

lenticular,  134 

Lieberkuehn,  138 

lingual,  129 

Litre's,  181,  182 

Luschka's,  109 

mammary,  240 

Meibomian,  294 

mixed,  57,  154 

Moll,  294 

Montgornmery's,  243 

mucous,  56,  154 

olfactory,  312 

pancreas,  155 

parathyroids,  170 

parotid,  155 

peptic,  136 

pineal,  252 

pituitary,  251 

preputial,  199 

prostate,  196 

pyloric,  136 

racemose,  55 

saccular,  55 

salivary,  153 

sebaceous,  240 

serous,  56,  154 

structure  of,  154 

sublingual,  157 

submaxillary,  158 

sudoriparous,  239 

suprarenal,  183 

sweat,  239 

tarsal,  294 

tear,  296 

thymus,  116 

thyroid,  168 

tubular,  53 

tubulo-alveolar,  55 

Tyson's,  199 

unicellular,  52 

urethral,  181 


340 


INDEX. 


Glands 

uterine,  210 

varieties  according  to  outlet,  57 

secretion,  56 

structure,  53 

Glandular  cells,  50 

Glans,  clitoris,  216 

penis,  199 

Glassy  membrane,  278 
Glisson's  capsule,  148 
Globular  process,  320 
Glomerular  layer  of  olfactory  lobe,  250 

adrenal,  183 
Glomerulus,  173 
Glomus  caroticum,  no 

coccygeum,  109 
Glycerin  albumen,  29 

jelly,  24 

Glycogen,  32,  150 
Goblet  cells,  9,  134,  138,  142 
Gold  chlorid,  17 

stain,  17 
Golgi  cells,  86 

fixing  solution,  4 

silver  stain,  17 
Goll,  columns  of,  270 
Gower,  columns  of,  269 
Graafian  follicles,  201 
Granular  cells  of  cerebellum,  234 
Granule  cells  of  Graafian  follicle,  201 
Gray  commissure,  267 

substance,  84,  246 
Ground  substance  of  cartilage,  67 

of  bone,  70 
Growth,  35 

Gubernaculum  dentis,  332 
Gum,  10 
Gustatory 

hair,  127 

organ, 127 

pore,  127 

Hair 

auditory,  303 

bulb,  235 

color  of,  237 

follicle,  235 

lanugo,  237 

layers  of,  236 

muscle,  237 

olfactory,  281 

papilla,  235 

root,  235 

root-sheaths,  236 
.  shaft,  235 
Hair-cells,  301,  307 
Hardening  agent,  5 
Hassal's  corpuscles,  117 
Haversian  canals,  71 

lamellae,  71 
Heart,  88 

annuli  fibrosi,  96 

blood-vessels  of,  98 

bundle  of  His,  97 

chordae  tendineae,  97 

corpus  Arantii,  97 

elastic  tissue,  96 

endocardium,  96 

epicardium,  98 


Heart 

lymphatics,  98 

muscle,  82 

myocardium,  98 

nerves  of,  98 

pericardium,  98 

structure  of,  96 

valves,  97 
Heidenhain,  demilunes  of,  158 

solution,  i 

Helicine  arteries,  199 
Hematoidin  crystals,  109 
Hematoxylin,  acid,  13 

Delaneld's,  13 

Harris',  12 

Weigert's,  19 
Hemin  crystals,  109 
Hemaglobin  crystals,  109 
Hemolymph  nodes,  no 
Henle's,  fenestrated  membrane  of,  101 

fibre  layer,  284 

layer,  236 

loop,  174 

limbs,  174 
Hensen's  cells,  306 

disc,  78 
Hiatus,  145 
Howship's  lacunae,  71 
Humor,  aqueous,  288 

vitreous,  288 
Huxley's  layer,  236 
Hyaloid  artery,  288 

canal,  288 

membrane,  288 
Hyalin  cartilage,  67 

cells,  107 
Hyaloplasm,  31 
Hymen,  215 
Hypoblast,  41 
Hypophysis,  251 

Ileum,  142 
Indirect  division,  36 
Infiltration  angle,  281 

celloidin,  9 

gum,  10 

paraffin,  7 
Injection,  24 
Inner  cell-mass,  42,  217 
Inner  bulb,  92,  285 
Intercellular  bridges  (spines),  48,  230 

substance,  59,  62,  67,  70,  86 
Interfilar  mass,  31 
Interglandular  projection,  133 
Interglobular  spaces,  122 
Intermediate  disc,  79 
Internal  ear,  300 

elastic  lamina,  99 
Interstitial  cells  of  ovary,  201 

of  testicle,  189 
Intervillous  spaces,  226 
Intestine 

agminated  follicles  of,  142 

blood-vessels  of,  146 

Brunner's  glands,  142 

crypts  of,  138 

epithelium  of.  138 

goblet  cells  of,  138,  142,  144 

folds  of  Kerkring,  141 


INDEX. 


341 


Intestine 

large,  142 

lymphatics,  146 

mucosa  of  large,  142 
of  small,  138 

muscular  coat  of  large,  143 
of  small,  142 

nerves  of,  146 

Peyer's  patches  of,  142 

plica  circulates,  141 

solitary  follicles,  141 

submucosa  of  large,  143 
of  small,  142 

valyulae  conniventes,  141 

villi,  139 
Intima  of  artery,  99 

of  vein,  102 

Intra-cartilagenous  bone,  74 
Intrafusal  muscle  fibres,  92 
Intra-membranous  bone,  77 
Intumescentia  cervicalis,  263 

lumbalis,  263 
lodin,  29 
Iris 

anterior  endothelium,  279 
lamina,  280 

muscle,  280 

pigment,  280 

posterior  epithelium,  280 
lamina,  280 

strorna,  279 
Irritability,  36 
Islands,  pancreatic,  156 
Isotropic,  78 

Jejunum,  142 
Jelly,  glycerin,  24 
Wharton's,  208 

Karyokinesis,  37 
Karyolymph,  33 
Karyosomes,  33 
Katabolism,  35 
Keratohyalin,  231 
Kerkring,  folds  of,  141 
Kidney 

arched  tubules,  175 

arches,  arterial,  177 
venous,  178 

blood-vessels  of,  176 

Bowman's  capsule,  173 

capsule  of,  171 

columns  of  Bertin,  173 
of  Ferrein,  172 

convoluted  tubules,  174 

cortex,  171 

ducts  of  Bellini,  175 

Henle's  limbs,  174 
loops,  174 

hilus,  171 

interjobular  arteries,  177 
veins,  177 

labyrinth,  173 

lymphatics,  178 

pyramids,  173 

medulla,  173 

medullary  pyramids,  173 
rays,  172 


Kidney 

nerves  of,  178 

papillary  ducts,  175 

pyramids,  medullary,  173 
of  Ferrein,  172 

renal  corpuscle,  173 

sinus  of,  171 

straight  collecting  tubules,  175 

tubules,  174 

diameter  of,  173 

uriniferous,  174 

venae  stellatae,  177 
Kopsch's  fluid,  3 
Krause,  corpuscles  of,  317 

gland  of,  294 

membrane  of,  79 

Labia  majora,  216 

minora,  215 
Labyrinth,  bony,  301 

membranous,  301 

of  kidney,  173 
Lacrimal  apparatus,  296 

canaliculi,  296 

caruncle,  295 

gland;  296 

accessory,  294 

sac,  296 
Lacteal,  140 
Lacunae,  bone,  72 

corneal,  275 

Howship's,  67 

trophodermal,  222 
Lamellae  of  bone 

circumferential,  70 

concentric,  71 

external,  70 

ground,  72 

Haversian,  71 

intermediate,  72 

internal,  72 

perimedullary,  72 

periosteal,  70 

peripheral,  70 

Lamellar  corpuscles,  91,  3,16 
Lamina 

cribrpsa,  274 

elastic,  anterior,  275 
external,  99 
internal,  99 
posterior,  276 

fusca,  274 

spiralis,  305 

suprachoroidea,  277 
Langerhans,  areas  of,  156 
Langhans,  layer  of,  224 
Lantermann,  clefts  of,  87 
Lanugo  hairs,  237 
Large  intestine,  142 
Larynx 

blood-vessels  of,  161 

cartilages  of,  160 

coats  of,  159 

epiglottis,  159 

nerves  of,  161 

ventricles,  160 

vocal  cords,  160 
Lateral  discs,  73 


342 


INDEX. 


Lateral  lemniscus,  258 
Lens,  crystalline,  288 

capsule  of,  288 

epithelium  of,  289 

fibres  of,  289 

ligaments  of,  289 
Lenticular  glands  (follicles),  134 
Leukocytes 

classification  of,  105 
Leydig's  cells,  189 
Lieberkuehn's  glands,  138 
Ligamentum  nuchae,  62 

pectinatum,  276 

spirale,  305 

suspensorium,  259 
Limbus,  306 
Limiting  membrane  of  retina 

external,  284 

internal,  286 
of  vessels 
of  arteries,  99 
of  veins,  102 
Lingual 

glands,  129 

papillae,  127 

septum,  129 

tonsil,  129 

Lines  of  Schreger,  120 
Linin,  33 
Lip,  118 
Liquor  folliculi,  204 

sanguinis,  108 
Lithium  carbonate,  19 
Litre",  glands  of,  181,  182 
Liver 

bile-capillaries,  150 

blood-vessels,  of,  150 

capsule,  148 

cells,  150 

circulation  of,  151 

function  of,  152 

hepatic  duct,  153 

interlobular  ducts,  150 
tissue,  150 
vessejs,  150 

lobule,  148 

lymphatics,  152 

nerves  of,  152 

pig's,  148 

portal  system,  150 
vein,  151 

reticulum  of,  148 
Loop,  Henle's,  174 
Lungs 

air-sacs,  166 

alveolar  ducts,  166 

alvei,  1 66 

alveoli,  166 

blood-vessels  of,  167 

circulation  of,  167 

lobules,  165 

lymphatics,  167 

nerves  of,  168 

pleura,  163 

respiratory  bronchiole,  165 
epithelium,  165 

terminal  bronchiole,  165 

vestibulum,  166 


Lunula,  97,  238 
Luschka's  gland,  109 
Lutein 

cells,  201 

Lymphatic  system,  112 
Lymph  capillaries,  112 

ducts,  112 

vessels,  112 
Lymph  follicles 

agminated,  66,  142 

germinal  center  of,  66,  142 

of  appendix,  144 

of  intestine,  141,  142 

of  pharynx,  131 

of  tongue,  129 

of  tonsil,  129 

solitary,  66,  129 
Lymph  node 

blood-vessels  of,  114 

cortex,  112 

hilus,  114 

lymph  sinuses,  114 

medulla,  113 

medullary  cords,  113 

nerves,  114 

structure  of,  112 
Lymphocytes,  107 
Lymphoid  tissue 

dense,  66,  112 

diffuse,  65,  112 

M. 

Macroblast,  106 
Macrocyte,  105 
Macula  acustica,  301 

lutea,  287 

Male  genital  organs,  186 
Malformations  of  face,  322 

of  palate,  322 

of  teeth,  332 
Malpighian  body,  173 

corpuscles,  115 

pyramid.  174 
Mammary  gland 

ampulla,  242 

areola,  243 

cells  of,  242 

colostrum,  243 

glands  of  Montgommery,  243 

lactating  and  nonlactating,  242 

nerves  of,  243 

nipple,  243 

structure  of,  241 
Mammilla,  243 
Margarin  crystals,  64 
Marrow 

cells  of,  73 

cavity,  72 

red,  73 

serous,  73 

spaces,  74 

yellow,  73 
Marrow  cells,  73 
Mast-cells,  108 
Matrix  of  nail,  238 

cartilage,  67 

Maturation  of  ovum,  40,  204 
Mayer's  albumen,  28 

solution,  ii 


INDEX. 


343 


Media,  of  artery,  99 

of  vein,  102 
Medial  lemniscus,  258 
Median  disc  of  Hensen,  78 
Median  longitudinal  bundle,  258. 
Mediastinum  testis,  186 
Medullary  cavity,  72 

cords,  113 

pyramids,  173 

rays,  172 

sheaths,  87 
Medulla 

of  adrenal,  184 

of  bone,  72 

of  cerebellum,  255 

of  cerebrum,  249 

of  hair,  237 

of  kidney,  173 

of  lymph  node,  113 

of  ovary,  207 
Meibomian  glands,  294 
Meissner's  corpuscles,  91,  315 

plexus,  146 
Membrana  basilaris,  306 

nictitans,  295 

olfactoria  limitans,  312 

preformativa,  326 

reticularis,  307 

tectoria,  309 
Membrane 

basement,  50 

basilar,  306 

Bowman's,  275 

Corti's,  309 

Descemet's,  276 

fenestrated,  of  Henle,  101 

glassy,  278 

hyaloid,  288 

Krause,  79 

mucous,  50 

Nasmyth's,  126 

otolith,  271 

peridental,  125,  328 

of  cell,  34 

of  retina  external  limiting,  284 
internal  limiting,  286 

Reissner,  304 

serous,  51 

tympanic,  298 

vitelline,  40,  203 
Menisci,  90 

Menstruation,  changes  of,  212 
Mesoblast,  42 
Mesoderm,  42,  218 

derivatives,  43 
Mesothelium,  51 
Metabolism,  35 
Metaphase,  39 
Methylene  blue,  14 
Methyl  green,  14 
Microblast,  106 
Microcyte,  105 
Microsome,  32 
Middle  ear,  299 
Milk,  242 
Mitosis,  37 
Mitral  cells,  250 
Mixed  connective  tissue,  64 


Mixed  glands,  57,  154 
Modiolus,  303 
Molecular  layer 

of  cerebellum,  254 

of  cerebrum,  247 

of  olfactory  bulb,  250 

of  retina,  284,  286 
Moll,  glands  of,  294 
Monaster,  38 
Mons  veneris,  216 
Montgommery's  glands,  243 
Morula,  42 
Mossy  cells,  86 
Mother  cell,  189 

star,  38 
Motion,  35 
Motor  cells,  265 

endings,  94 

nerves,  87 

roots,  271 
Mounting,  29 
Mouth,  119 
Mucin,  49,  138 
Mucous  connective  tissue,  62 

glands,  56,  154 

membrane,  50 
Mulberry  mass,  42 
Mueller's  fibres,  284 

lid  muscle,  294 

ring  muscle,  279 

solution,  2 
Muscle 

nerves  of,  83,  94 

of  blood-vessels,  81 

structure  of  a,  81 

vein,  1 02 
Muscle  fibre 

branched,  82 

cardiac,  82 

Cohnheim's  fields,  79 

fibrillae  of,  75 

involuntary,  81 

nuclei,  79,  80,  82 

pigment  in,  82 

red,  79 

sarcolemma,  79 

sarcoplasm,  78 

sarcous  elements,  78 

smooth,  8 1 

striations,  79,  81,  82 

voluntary,  78 

white,  79 
Muscle-spindle,  92 
Muscularis  mucosae,  50 
Myelin  sheath,  87 

stain,  19,  20 
Myelocyte,  73,  108 
Myeloplaxes,  73 
Myocardium,  98 

Nabothi,  ovuli,  210 
Nails 

bed,  238 

body,  238 

eponychium,  238 

fold,  237 

groove,  238 

lunula,  238 


344 


INDEX. 


Nails 

matrix,  238 

root,  237 

wall,  237 
Nares,  159 
Nasal  mucosa 

blood-vessels  of,  313 

Bowman's  glands,  312 

lymphatics,  313 

nerves  of,  313 

olfactory  area,  311 

respiratory  portion,  311 
Nasmyth's  membrane,  126 
Nasof rental  process,  320 
Nerve  cells 

axis-cylinder,  84 

bipolar,  85 

Deiter's,  86 

dendrites,  84 

first  type,  86 

Golgi's,  86 

multipolar,  86 

neurit,  84 

neuron,  84 

second  type,  86 

structure,  84 

telodendrites,  85 

unipolar,  85 
Nerve-organs 

bulbs,  90 

classification,  90 

conjunctival,  91,  317 

corpuscles  of  Meissner,  91,  315 
of  Vater,  91,  316 
of  Wagner,  91,  315 

genital,  91,  317 

in  epithelium,  90 
smooth  muscle,  95 
voluntary  muscle,  94 

motor,  94 

neuro-muscular,  92 

neuro-tendinous,  94 

Pacinian  body,  91,  315 

sensor,  90 

tactile  cells,  90 

corpuscles,  90,  315 
Nerve  fibre 

amyelinated,  89 

axis-cylinder,  87 

functional  varieties,  87 

internode,  87 

myelin,  87 

myelin  sheath,  87 

myelinated,  87 

neurilemma,  87 

nodes  of  Ranvier,  87 

sheath  of  Schwann,  87 

sympathetic,  89 

white  substance  of  Schwann,  87 
Nerve  trunk 

blood-vessels  of,  89 

endoneurium,  89 

epineurium,  89 

sympathetic,  89 

lymphatics,  89 

perineurium,  89 

system,  245 

tissues,  84,  246 


Nerve  nervorum,  89 

yasorum,  100 
Neurilemma,  87 
Neuro-epithelium 

of  ear,  301,  307 

of  eye,  282 

of  nose,  312 

of  retina,  282 

of  taste  buds,  127,  314 
Neurofibrils,  84 
Neuroglia,  86,  246 

cells  of,  86 

fibres,  86 
Neuron,  84 
Neutrophil,  97 
Nissl's  bodies,  84 
Nitric  acid,  4 
Nodes  of  Ranvier,  87 
Nodules 

cortical,  112 

lymph,  66,  112 

secondary,  112 

solitary,  66,  112 
Normoblasts,  106 
Nuclear 

division,  37 

matrix,  33 

membrane,  33 

sap    33 

spindle,  39 
Nucleolus,  34 
Nucleus,  32 

achromatin,  33 

arcuate,  262 

chromatin,  33 

cuneatus,  261 

gracillis,  260 

olivary,  inferior,  262 
superior,  258 

of  lateral  lemniscus,  258 

Stilling,  267 
Nuel,  spaces  of,  309 
Nutritive  yolk,  203 
Nymphae,  214 


Oblongata,  258 

Odontob lasts,  124,  327 

Oils  for  clearing 
anilin,  23 
anilin-xylol,  23 
bergamot,  22 
benzol  of,  22 
cedar-wood,  6,  22 
clove,  22 
creosote,  22 
origanum,  22 
turpentine,  6 
toluol,  7,  22 
xylol,  6,  22 

Olfactory  lobe 

glomerular  layer,  250 
granular  layer,  250 
mitral  cells,  250 
molecular  layer,  250 
peripheral  fibres,  250 

Olfactory  mucosa 

blood-vessels  of,  313 


INDEX. 


345 


Olfactory  mucosa 

cells  of,  311 

glands  of,  312 
Olivary  bodies,  262 

nucleus,  258,  262 
Oocyte,  204 
Optic  nerve,  287 

papilla,  287 
Orange,  15 
Ora  serrata,  287 
Oral  cavity,  119 

depression,  318 
Organ  of  Corti,  307 
Orth's  solution,  3 
Osmic  acid  fixative,  3 

stain  for  fat,  21,  65 
Osteoblasts,  70 
Osteoclasts,  73 
Ossicles,  auditory,  299 
Ossification 

endochondral,  74 

intra-membranous,  77 
Otolith  membrane,  302 
Otoliths,  302 
Outer  cell-mass,  217 
Ovary 

antrum  of  follicle,  202 

blood-vessels  of,  207 

corpus  albicans,  206 
hemorrhagicum,  206 
luteum,  206 

cortex,  201 

egg  tubes  of  Pflueger,  204 

germinal  epithelium,  201 

Graafian  follicle,  201 

hilus,  201 

interstitial  cells,  207 

lymphatics,  207 

medulla,  207 

muscle  tissue  of,  207 

nerves  of,  208 

tunica  albuginea,  201 
Oviduct,  208 
Ovulation,  207 
Ovuli  Nabothi,  210 
Ovum 

dentoplasm,  40,  203 

embryologic,  41 

escape  of,  206,  207 

fertilization,  41 

formative  yolk,  40,  207 

maturation,  40,  205 

nutritive  yolk,  40,  207 

segmentation,  42 

structure,  40,  207 
Oxyntic  cell,  134 
Oxyphil,  see  Eosinophil 

Pacchpnian  bodies,  245 

villi,  245 

Pacinian  bodies,  91,  316 
Palate,  development  of,  322 
Palatine  tonsils,  129 
Pancreas 

areas  of  Langerhans,  156 

blood-vessels  of,  155 

cells  of,  154 

centro-acinar  cells,  155 


Pancreas 

ducts,  154 

nerves  of,  155 

zympgen  granules,  154 
Pancreatic  duct,  156 
Panniculus  adiposus,  233 
Papilla 

circumvallate,  127 

filiform,  126 

foliate,  314 

fungiform,  127 

hair,  235 

of  mucosa  of  tongue,  126 
esophagus,  131 

optic,  287 

tactile,  232 

vascular,  232 
Paracarmin,  16 
Paradidymis,  199 
Paraffin 

fixation  of,  sections,  28 

infiltration,  7 

removal  from  sections,  29 

sectioning,  10 
Parathyroids,  170 
Parasympathetics,  no 
Paroophoron,  208 
Parotid  gland,  155 
Parovarium,  208 
Pars  ciliaris  retinas,    278 

iridica  retinae,   280 

pptica  retinae,  281 
Pectinate  ligament,  281 
Pellicula,  34 
Pelvis  of  ureter,  170 
Penis 

arteries  of,  199 

corpora  cavernosa,  198 

corpus  spongiosum,  199 

emissary  veins,  199 

erectile  tissue,  198 

glands  of  Tyson,  199 

glans,  199 

helicine  arteries,  199 

nerves,  199 

tunica  albuginea,  198 

veins,  199 
Peptic  cells,  14,  134 

glands,  136 
Perforating  fibers  of  cornea,  275 

of  Sharp  ey,  69 
Pericardium,  98 
Perichondrium,  66 
Peridental  membrane,  125 
Perimysium,  81 
Perineurium.  89 
Periosteal  lamellae,  70 
Periosteum,  69 
Peripheral  nerve  organs,  82 
Peritendineum,  61 
Perivitelline  space,  203 
Petit's  canal,  289 
Peyer's  patches,  66,  142 
Pflueger's  egg  tubes,  204 
Phagocytes,  107 
Phalangeal  plates,  307 

process,  307 
Pharynx,  130 


346 


INDEX. 


Phloroglucin — nitric  acid,  n 
Pia,  245 

Picric  acid  stain,  14 
Picro-carmin,  16 
Picro-fuchsin,  15 
Pigment  cells,  50 

of  hair,  237 

of  iris,  280 

of  retina,  282 

of  skin,  233 
Pig's  liver,  148 
Pillar  cells,  307 
Pineal  body,  252 
Pinna,  298 
Pits,  gastric,  133 
Pituitary  body,  251 
Placenta 

canalized  fibrin,  226 

cell-knots,  224 

chorion,  226 

decidua,  217 

development  of,  219 

intervillous  spaces,  226 

septa  of,  224 

syncytium,  222 

villi  of,  223 
Placentoblast,  219 
Plasma  cells,  59 
Plastids,  32 
Platelets  of  blood,  108 
Pleura,  163 
Plexus  of  Auerbach,  146 

of  Meissner,  146 
Plica 

circulares,  141 

palmatae,  210 

semilunaris,  295 
Polar  bodies,  42,  204 

field,  38 

Polynuclear  cells,  106 
Polyphyodonts,  322 
Pons,  255 
Pontile  nuclei,  255 
Portal  circulation,  150 

system,  1.50 

vein,  150 

Posthypophysis,  251 
Postoblongata,  258 
Potassium  bichromate,  2 
Pouches,  visceral,  319 
Precapillary  vessels,  101 
Prehypophysis,  251 
Preoblongata,  257 
Prepuce,  198 
Prickle  cells,  4,  230 
Primary  marrow  cells,  75 

spaces,  75 
Prochorion,  219 
Prominentia  spiralis,  305 
Prophase,  37 
Prostate 

blood-vessels,  196 

capsule,  196 

glands,  196 

nerves,  197 
Prostatic  bodies,  196 
Protoplasm,  31 
Prussian  blue,  24 


Pseudostratified  cells,  48 
Pulp  cavity,  119 

splenic,  115 

tooth,  123 
Pupil,  280 
Purkinje  cells,  254 
Pyramidal 

cells  of  cerebrum,  249 

columns,  direct,  269 

crossed,  270 
Pyramids 

Malpighian,  173 

medullary,  173 

of  Ferrein,  172 
Pyramidal 

decussation,  359 
Pyramis,  263 
Pyrenin,  34 


Ranyier,  nodes  of,  87 
Rapid  technic,  28 
Receptaculum  chyli,  146 
Rectum,  143 

valves  of,  143 
Red  blood  cells,  102 

bone  marrow,  73 
Reissner's  membrane,  304 
Remak's  fibres,  89 
Renal  corpuscles,  173 
Reproduction,  36 
Respiratory 

bronchiole,  165 

organs,  159 
Restiform  bodies,  262 
Rete  Malpighii,  230 

testis,  189 
Retia  mirabilia,  102 
Reticular  connective  tissue,  63 

gland,  58 
Reticulum,  63 
Retina 

amakrine  cells,  285 

blind  spot,  286 

blood-vessels,  289 

central  artery,  289 

cone-cells,  282 

cone-fibres,  282 

fovea  centralis,  287 

ganglion  cells,  285,  286 

Henle's  fibre  layer,  284 

limiting  membrane,  inner,  286 
outer,  284 

macula  lutea,  287 

molecular  layer,  inner,  286 
outer,  284 

nerve  fibre  layer,  286 

optic,  281 

optic  nerve  papilla,  287 

ora  serrata,  287 

pars  ciliaris,  278 
iridica,  280 
optica,  281 

pigment  layer,  282 

rhodopsin,  284 

rod-cells,  283 
fibres,  284 

visual  purple,  284 


INDEX. 


347 


Rod-cells,  283 
fibres,  284 

Rolandi,  substantia  gelatinosa,  268 
Root  sheaths,  236 
Rouleaux,  105 

Sacculations  of  colon,  142 

Sacculus,  301 

Safranin,  14 

Salivary  corpuscles,  129 

glands,  153 
Sarcolemma,  79 
Sarcoplasm,  78 
Scala  media,  303 

tympani,  303 

vestibuli,  303 
Schlemm's  canal,  281 
Schwann,  sheath  of,  87 

white  substance  of,  87 
Sclera,  274 

Scleral  conjunctiva,  295 
Sebaceous  glands,  240 
Sebum,  240 

Secondary  marrow  spaces,  75 
Secretion,  56 

Secretory  canals,  136,  150,  155 
Sectioning  celloidin,   n 

paraffin,  10 

Sections,  staining  of,  29 
Semen,  194 

Semi-circular  canals,  303 
Seminiferous  tubules,  188 
Seminal  vesicles,  195 
Sense  of  smell,  311 

taste,  314 

touch,  315 
Sensor  decussation,  262 

nerves,  87 

organs,  90 

Septa,  placental,  205 
Septum  linguali,  129 

posterior  median,  238 
Serous  glands,  56,  154 

membranes,  51 
Sertoli's  columns,  189 
Sharpey's  fibres,  69 
Sheath,  Henle's,  217 

Huxley's,  217 

myelin,  87 
Silver  staining 

blood-vessels,  19 

lymphatics,  19 

nerve  tissue,  17 
Sinus  lactiferous,  243 

marginal,  227 

lymph,  114 

of  kidney,  171 
Sinusoids,  102 
Skein,  daughter,  40 

mother,  37 
Skin 

appendages,  234 

arrector  pili  muscle,  237 

blood-vessels  of,  233 

color  of,  233 

corium,  231 

derma,  231 

epidermis,  230 


Skin 

glands,  239 

layers  of,  230 

lymphatics,  234 

panniculus  adiposus,  233 

pigment,  233 
Slide  technic,  28 
Slides,  28 

Small  intestine,  138 
Smell,  311 
Smooth  muscle,  81 
Sole-plate,  95 
Solitary  follicles,  66 
Somatopleure,  218 
Spaces  of  Fontana,  281 

of  Nuel,  309 
Spermid,  193 
Spermioblast,  194 
Spermiocyte,  193 
Spermiogenesis,  192 
Spermiogonia,  188,  192 
Spermatozoon,  42 
Spider  cell,  86 
Spinal  cord 

blood-vessels  of,  273 

canal,  267 

cells,  265 

commissures,  267,  268 

columns,  269 

fissure,  263 

functional  divisions  of,  271 

gray  substance,  264 

horns,  265 

membranes  of,  245 

nerves,  271 

septum,  264 

white  substance,  268 
Spindle,  central,  39 

nuclear,  39 
Spinal  ganglion,  271 
Spirem,  37 

Splanchnopleure,  218 
Spleen 

capsule,  114 

circulation,  116 

corpuscles,  115 

lobules,  104 

Malpighian  corpuscles,  115 

pulp,  115 

trabeculas,  115 
Spongioplasm,  31 
Spongy  bone.  70 
Spot,  germinal,  41 
Staining  of  sections,  12,  29 
Stains 

acid,  14 

acid  hematoxylin,  13 

alum  carmin,  15 

anilin  dyes,  13,  14 

basic,  12 

Bismarck  brown,  14 

borax  carmin,  15 

carmin,  15 

Delafield's  hematoxylin,  13 

Ehrlich-Biondi-Heidenhain,  16 

elastica,  21 

eosin,  14 

eosin-methylene  blue,  27 


348 


INDEX. 


Stains 

for  adipose  tissue,  59 

gold,  17 

Harris'  hematoxylin,  12 

hematoxylin  acid,  13 
Delafield's  13 
Harris',  12 

methylene  blue-eosin,  27 

methyl  green,  14 

myelin,  19,  20 

nuclear,  12 

orange,  15 

osmic  acid  for  fat,  21,  65 

paracarmin,  16 

picric  acid,  14 

picro-carmin,  16 

protoplasmic,  14 

silver,  17 

safranin,  14 

Sudan  III  for  fat,  21,  65 

Van  Gieson,  15,  21 

Weigert's  elastica,  21 
myelin,  17 

Weigert-Pal,  20 

Wright's  blood,  26 
Stars,  daughter,  40 

mother,  38 
Stellate  cells,  58 
Stomach, 

acid  cells,  135 

blood-vessels,  137 

cardiac  end,  134 

coats,  133 

glands,  133 

lymphatics,  137 

mucous  membrane,  133 

nerves,  138 

peptic  cells,  134 

pyloric  end,  136 
Stratum  corneum,  230 

germinativum,  230 

granulosum,  231 
of  ovary,  202 

intermedium,  325 

lucidum,  231 

Malpighii,  230 

mucosum,  230 

papillare,  231 

reticulare,  232 

supra vasculare,  211 

vasculare,  210 
Stria  vascularis,  305 
Striae  of  Retzius,  120 
Striations  of  Baillarger,  247 

of  Bechtereff,  247 
Stilling 

canal  of,  288 

nucleus  of,  240 
Stomodeum,  318 
Subarachnoid  space,  245 
Subdural  space,  245 
Subscleral,  274 
Sublingual  gland,  157 
Submaxillary  gland,  158 
Substantia  gelatinosa,  259,  267 

grisea  centralis,  268 

propria,  275 

spongiosa,  268 


Subzonal  ectoderm,  217 
Succus  entericus,  142 
Sudan  III,  21,  65 
Sudoriparous  glands,  239 
Sulcus  spiralis,  306 
Suprarenal  body 

blood-vessels,  184 

cells,  183 

cortex,  185 

medulla,  184 

nerves,  185 

zones,  183 

Suspensory  ligaments  of  lens,  289 
Sustentacular  cells,   127,  189,  302,  309, 

3ii,  3i4 
Sweat-glands 

blood-vessels,  243 

cells  of,  239 

lymphatics,  244 

modified,  240 

nerves,  243 

pore,  239 
Syncytium,  226 

Tactile  cells,  90 

corpuscles,  90,  315 

menisci,  90 

papillae,  231 
Taenia  coli,  143 
Tapetum  cellulosum,  278 

fibrosum,  277 
Tarsal  glands,  294 

plates,  293 
Taste-buds,  127,  159,  314 

pore,  127 

sense  of,  314 
Tear  gland,  296 

accessory,  294 
Technic,  general,  i 

rapid,  28 

slide,  28 
Teeth,  auditory,  306 

cementum,  123 

crown,  119 

dentin,  120 

development  of,  322 

enamel,  120 

fang,  119 

nerves,  124 

pulp,  123 

root,  119 

root  canal,  119 

vessels  of,  124 
Teichmann's  crystals,  109 
Tellyesnicky's  solution,  2 
Telophase,  40 
Tendon,  61 

cells,  6 1 
Tenon,  capsule  of,  297 

space  of,  292 

Terminal  bronchioles,  166 
Testicle 

blood-vessels,  190 

excretory  tubules,  189 

interstitial  cells,  189 

lobules  of,  1 86 

lymphatics,  190 

mediastinum,  186 


INDEX. 


349 


Testicle 

nerves,  190 

seminiferous  tubules,  188 

tunica  albuginea,  186 

vaginalis,  186 
Theca  folliculi,  202 
Third  eyelid,  295 
Thrombocytes,  108 
Thymus 

blood-vessels,  117 

changes  in,  116 

corpuscles  of  Hassal,  117 

cortex,  117 

medulla,  117 
Thyroid  body 

blood-vessels,  170 

colloid  substance,  169 

lymphatics,  170 
Tigroid  bodies,  84 
Tissue 

areolar,  64 

adipose,  64 

connective,  58 

definition  of,  45 

elastic,  62 

embryonic,  62 

epithelial,  45 

erectile,  198,  215 

fibrous,  58 

lymphoid,  63 

mucous,  62 

muscle 

cardiac,  82 
smooth,  8 1 
voluntary,  78 

nerve,  84 

retiform,  63 
Toluol,  8,  22 

Tome's  granular  layer,  122 
Tongue 

blood-vessels,  129 

glands,  129 

lymphoid  tissue,  129 

muscle,  126 

papillae,  126 

taste-buds,  127 
Tonsil 

crypts  of,  129 

lingual,  129 

palatine,  129 
Touch,  315 
Trachea,  161 
Transitional  cells,  49 
Trichloracetic  acid,  n 
Trigonum  vesicae,  181 
Triploblast,  42,  217 
Trophoderm,  218 
Trophodermal  lacunas,  220 
Tuberculum  Rolandi,  259. 
Tubular  glands 

coiled,  53 

compound,  53 

branched,  53 

reticular,  54 

simple,  50 
Tubules 

dentinal,  122 

intercalated,  15 


Tubules 

intermediate,  154 
secretory,  154 
seminiferous,  188 
uriniferous,  174 
Tubuli  recti,  189 
Tubulo-alveolar  glands,  55 
Tunica  adyentitia,  99 

albuginea  ovary,  2-01 

testicle,  186 
externa  artery,  99 
eye,  274 
vein,  102 
interna  artery,  99 
eye,  274 
vein,  102 
media  artery,  99 
eye,  274 
vein,  102 
propria,  50 
vaginalis,  186 
Tunica  vasculosa,  202 
Tunnel  of  Corti,  307 
Turpentine,  6 
Tympanic  cavity,  299 
lamella,  306 
membrane,  298 
Tympanum,  299 
Tyson's  glands,  199 

Umbilical  cord,  227 
Units,  functionating,  154 

secreting,  154 

structural,  154 
Ureter,  180 
Urethra 

female,  181 

male,  181 
Urinary  bladder,  180 

organs,  171 

Uriniferous  tubule,  174 
Uterus 

blood-vessels  of,  213 

cervix,  210 

glands,  210 

lymphatics,  213 

menstrual  changes,  212 

mucosa,  210 

nerves,  213 

ovuli  Nabothi,  210 
Utriculus,  301 
Uveal  tract,  276 

Vacuoles,  32 
Vagina,  213 
Valves  of  heart,  97 

veins,  102 

Valvulae  conniventes,  141 
Van  Gilson's  stain,  15,  21 
Vasa  efferentia,  189 

vasorum,  100 
Vascular  papillae,  232 
Vas  deferens,  195 
Vater-Pacinian  body,  91,  316 
Veins 

central,  148 

coats  of,  102 


INDEX. 


Veins 

portal,  150 

valves  of,  102 
Venae  archiformes,  178 

rectae,  178 

stellatae,  177 

vprticosae,  201 
Ventricles  of  larynx,  160 
Vermiform  appendix,  143 
Vesicle 

blastodermic,  42 

entodermal,  218 

germinal,  40,  203 

seminal,  195 
Vestibule 

of  vagina,  2 1 5 
Villi  chorionic,  223 

of  oviduct,  208 

of  placenta,  226 

Pacchionian,  245 

of  small  intestine,  139 
Visceral  arches 

changes  in,  318,  319,  320 

derivatives  of,  319,  320 
Visceral  pouches,  319,  320 
Visual  cells,  284 
Visual  purple,  284 
Vital  phenomena,  34 
Vitelline  membrane,  40,  203 
Vitellus,  40,  203 
Vitreous  humor,  288 
Vocal  cords,  160 
Volkmann's  canals,  71 
Voluntary  muscle,  78 

Wagner,  corpuscles  of,  91,  315 
Wandering  cells,  59 


Weigert's  elastica  stain,  21 
Weigert's  myelin  stain,  19 
Weigert-Pal  myelin  stain,  20 
Wharton's  duct,  158 

jelly,  27 
White  blood-cells,  105 

commissure,  268 

fibrous  tissue,  58 

substance,  86,  246 

substance  of  Schwann,  87 
Wirsung's  duct,  158 
Wright's  blood  stain,  26 

Xylol,  6,  22 

anilin  oil,  23 
balsam,  23 
carbol,  22 

Yellow  bone  marrow,  73 

elastic  tissue,  62 

fibre-cartilage,  68 

spot,  287 
Yolk,  formative,  203 

nutritive,  203 

Zenker's  fluid,  2 
Zinn,  zone  of  289 
Zona 

fasciculata,  183 

glomerulosa,  183 

granulosa,  202 

pellucida,  203 

reticularis,  184 
Zone,  boundary  of  choroid,  277 

kidney,  173 

of  Zinn,  289 


cA   Companion    Volume    io    Gould's    ^Pocket    'Dictionary 

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